Prolonged grief disorder: Psychometric validation of criteria proposed for DSM-V and ICD-11 — TEI-tagged view

Holly G. PrigersonpersName, Mardi J. HorowitzpersName, Selby JacobspersName, Colin Murray ParkespersName, Mihaela AslanpersName, Karl GoodkinpersName, Beverley RaphaelpersName, Samuel J. MarwitpersName, Camille B. WortmanpersName, Robert A. NeimeyerpersName, George A. BonannopersName, Susan D. BlockpersName, David W. KissanepersName, Paul A. BoelenpersName, Andreas MaerckerpersName, Brett T. LitzpersName, Jeffrey G. JohnsonpersName, Michael B. FirstpersName, Paul K. MaciejewskipersName (2009date). “Prolonged grief disorder: Psychometric validation of criteria proposed for DSM-V and ICD-11.” PLoS Medicinetitle·venue.

Object of study — A DIAGNOSTIC CATEGORY BEING BUILT: 4,785 CANDIDATE DEFINITIONS OF ONE DISORDER, ENUMERATED AND SCORED - prolonged grief disorderterm·def, proposed for DSM-V and ICD-11, whose symptom list and threshold are FITTED to data rather than agreed by a vote or counted across a literature

Research question — which griefterm symptoms are informative and unbiased enough to define a disorder, and which combination of them - how many, of which set, after how long - best separates cases from non-cases

Contribution — a six-phase psychometric procedure that reduces 22 candidate symptoms to 12, builds a criterion standardterm·def for 'caseness' where none existed, enumerates 4,785 candidate algorithms and selects one - yearningterm·def plus at least five of nine symptoms, at least six months after the death, with functional impairment

Full text — tagged

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277 plosmed PLoS Medicine PLoS Med PLOS PMC2711304 2711304 2711304 19652695 10.1371/journal.pmed.1000121 Prolonged Grief Disorderterm·def: Psychometric Validation of Criteria Proposed for DSM-V and ICD-11 PrigersonpersName Holly G 1 2 3 * HorowitzpersName Mardi J 4 JacobspersName Selby C 5 ParkespersName Colin M 6 AslanpersName Mihaela 7 GoodkinpersName Karl 8 9 RaphaelpersName Beverley 10 MarwitpersName Samuel J 11 WortmanpersName Camille 12 NeimeyerpersName Robert A 13 BonannopersName George 14 BlockpersName Susan D 1 2 3 KissanepersName David 15 BoelenpersName Paul 16 MaerckerpersName Andreas 17 LitzpersName Brett T 18 19 20 JohnsonpersName Jeffrey G 21 FirstpersName Michael B 21 MaciejewskipersName Paul K 1 2 Brayne Carol Academic Editor 22 1 Department of Psychiatry, Brigham and Women's Hospital, Boston, Massachusetts, United States of America 2 Center for Psycho-Oncology and Palliative Care Research, Dana Farber Cancer Institute, Boston, Massachusetts, United States of America 3 Harvard Medical School Center for Palliative Care, Boston, Massachusetts, United States of America 4 Department of Psychiatry, University of California School of Medicine, San Francisco, California, United States of America 5 Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut, United States of America 6 St. Christopher's Hospice, Sydenham, and St. Joseph's Hospice, Hackney, England 7 Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, United States of America 8 Department of Psychiatry and Behavioral Neurosciences, Cedars-Sinai Medical Center, Los Angeles, California, United States of America 9 Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California, United States of America 10 Department of Population Mental Health and Disasters, University of Western Sydney Medical School, New South Wales, Australia 11 Department of Psychology, University of Missouri, St. Louis, Missouri, United States of America 12 Department of Psychology, State University of New York at Stony Brook, New York, United States of America 13 Department of Psychology, The University of Memphis, Memphis, Tennessee, United States of America 14 Department of Counseling and Clinical Psychology, Teachers College, Columbia University, New York, New York, United States of America 15 Department of Psychiatry and Behavioral Sciences, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America 16 Department of Clinical and Health Psychology, Utrecht University, Utrecht, The Netherlands 17 Department of Clinical Psychology, University of Zürich, Zürich, Switzerland 18 Veterans Affairs Boston Healthcare System, Boston, Massachusetts, United States of America 19 National Center for PTSD, Boston, Massachusetts, United States of America 20 Boston University School of Medicine, Boston, Massachusetts, United States of America 21 Department of Psychiatry, Columbia University, New York, New York, United States of America 22 University of Cambridge, United Kingdom ✉ * E-mail: Holly_PrigersonpersName@dfci.harvard.edu ICMJE criteria for authorship read and met: HGP MJH SCJ CMP MA BR SJM CW KG RAN GB SDB DK PB AM BL JGJ MF PKM. Agree with the manuscript's results and conclusions: HGP MJH SCJ CMP MA BR SJM CW KG RAN GB SDB DK PB AM BL JGJ MF PKM. Designed the experiments/the study: HGP MJH PKM. Analyzed the data: PKM HGP MA. Collected data/did experiments for the study: HGP PKM. Enrolled patients: HGP. Wrote the firstpersName draft of the paper: HGP PKM. Contributed to the writing of the paper: HGP MJH SCJ CMP BR SJM CW RAN GB SDB DK PB AM JGJ MF PKM. Contributed to the conceptualisation: BR. Contributed items to the scale to assess PGDterm: CW. Assisted with interpretation of the results and contributed to the writing of the final manuscript, and reviewed and approved the contributions of others: RAN.

4 8 2009 6 8 e1000121 e1000121 4 8 2009 PrigersonpersName et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited. This article has been corrected. See PLoS Med. 2013 Dec 17;10(12):10.1371/annotation/a1d91e0d-981f-4674-926c-0fbd2463b5ea . See " Prolonged Grief Disorderterm·def: A Problem for the Past, the Present, and the Future ", e1000122. Holly PrigersonpersName and colleagues tested the psychometric validity of criteria for prolonged grief disorderterm·def (PGDterm) to enhance the detection and care of bereaved individuals at heightened risk of persistent distress and dysfunction.

Abstract Background Bereavementterm is a universal experience, and its association with excess morbidity and mortality is well established. Nevertheless, griefterm becomes a serious health concern for a relative few. For such individuals, intense griefterm persists, is distressing and disabling, and may meet criteria as a distinct mental disorder. At present, griefterm is not recognized as a mental disorder in the DSM-IV or ICD-10 . The goal of this study was to determine the psychometric validity of criteria for prolonged grief disorderterm·def (PGDterm) to enhance the detection and potential treatment of bereaved individuals at heightened risk of persistent distress and dysfunction.

Methods and Findings A total of 291 bereaved respondents were interviewed three times, grouped as 0–6, 6–12, and 12–24 mo post-loss. Item response theory (IRT) analyses derived the most informative, unbiased PGDterm symptoms. Combinatoric analyses identified the most sensitive and specific PGDterm algorithm that was then tested to evaluate its psychometric validity. Criteria require reactions to a significant loss that involve the experience of yearningterm·def (e.g., physical or emotional suffering as a result of the desired, but unfulfilled, reunion with the deceased) and at least five of the following nine symptoms experienced at least daily or to a disabling degree: feeling emotionally numb, stunned, or that life is meaningless; experiencing mistrust; bitterness over the loss; difficulty accepting the loss; identity confusion; avoidance of the reality of the loss; or difficulty moving on with life. Symptoms must be present at sufficiently high levels at least six mo from the death and be associated with functional impairment.

Conclusions The criteria set for PGDterm appear able to identify bereaved persons at heightened risk for enduring distress and dysfunction. The results support the psychometric validity of the criteria for PGDterm that we propose for inclusion in DSM-V and ICD-11 .

Please see later in the article for Editors' Summary Editors' Summary Background Virtually everyone loses someone they love during their lifetime. Griefterm is an unavoidable and normal reaction to this loss. After the death of a loved one, bereaved people may feel sadness, anger, guilt, anxiety, and despair. They may think constantly about the deceased person and about the events that led up to the person's death. They often have physical reactions to their loss—problems sleeping, for example—and they may become ill. Socially, they may find it difficult to return to work or to see friends and family. For most people, these painful emotions and thoughts gradually diminish, usually within 6 months or so of the death. But for a few people, the normal griefterm reaction lingers and becomes increasingly debilitating. Experts call this complicated griefterm or prolonged grief disorderterm·def (PGDterm). Characteristically, people with PGDterm have intrusive thoughts and images of the deceased person and a painful yearningterm·def for his or her presence. They may also deny their loss, feel desperately lonely and adrift, and want to die themselves.

Why Was This Study Done?

PGDterm is not currently recognized as a mental disorder although it meets the requirements for one given in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders , 4 th Edition (DSM-IV) and in the World Health Organization's International Statistical Classification of Diseases and Related Health Problems , 10 th Edition (ICD-10) . Before PGDterm can be recognized as a mental disorder (and included in DSM-V and ICD-11 ), bereavementterm and mental-health experts need to agree on standardized criteria for PGDterm. Such criteria would be useful because they would allow researchers and clinicians to identify risk factors for PGDterm and to find ways to prevent PGDterm. They would also help to ensure that people with PGDterm get appropriate treatments such as psychotherapy to help them change their way of thinking about their loss and re-engage with the world. Recently, a panel of experts agreed on a consensus list of symptoms for PGDterm. In this study, the researchers undertake a field trial to develop and evaluate algorithms (sets of rules) for diagnosing PGDterm based on these symptoms.

What Did the Researchers Do and Find?

The researchers used “item response theory” (IRT) to derive the most informative PGDterm symptoms from structured interviews of nearly 300 people who had recently lost a close family member. These interviews contained questions about the consensus list of symptoms; each participant was interviewed two or three times during the two years after their spouse's death. The researchers then used “combinatoric” analysis to identify the most sensitive and specific algorithm for the diagnosis of PGDterm. This algorithm specifies that a bereaved person with PGDterm must experience yearningterm·def (physical or emotional suffering because of an unfulfilled desire for reunion with the deceased) and at least five of nine additional symptoms. These symptoms (which include emotional numbness, feeling that life is meaningless, and avoidance of the reality of the loss) must persist for at least 6 months after the bereavementterm and must be associated with functional impairment. Finally, the researchers show that individuals given a diagnosis of PGDterm 6–12 months after a death have a higher subsequent risk of mental health and functional impairment than people not diagnosed with PGDterm.

What Do These Findings Mean?

These findings validate a set of symptoms and a diagnostic algorithm for PGDterm. Because most of the study participants were elderly women who had lost their husband, further validation is needed to check that these symptoms and algorithm also apply to other types of bereaved people such as individuals who have lost a child. For now, though, these findings support the inclusion of PGDterm in DSM-V and ICD-11 as a recognized mental disorder. Furthermore, the availability of a standardized way to diagnose PGDterm will help clinicians identify the minority of people who fail to adjust successfully to the loss of a loved one. Hopefully, by identifying these people and helping them to avoid the onset of PGDterm (perhaps by providing psychotherapy soon after a death) and/or providing better treatment for PGDterm, it should now be possible to reduce the considerable personal and societal costs associated with prolonged griefterm·var.

Additional Information Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000121 .

This study is further discussed in a PLoS Medicine Perspective by Stephen Workman The Dana Farber Cancer Institute has a page describing its Center for Psycho-oncology and Palliative Care Research The UK Royal College of Psychiatrists has a leaflet on bereavementterm (in English, Welsh, Urdu, and Chinese) The US National Cancer Institute also has information about coping with bereavementterm for patients and health professionals (in English and Spanish) MedlinePlus has links to other information about bereavementterm (in English and Spanish) The Journal of the American Medical Association has a patient page on abnormal griefterm Harvard Medical School provides a short family health guide about complicated griefterm Information on DSM-IV and ICD-10 is available status released display-pdf yes is-olf no is-manuscript no is-preprint no is-journal-matter no is-scanned no is-retracted no Received 2008 Mar 10; Accepted 2009 Jun 25; Collection date 2009 Aug.

Introduction Bereavementterm is a universal experience to which most individuals adequately adjust. Nevertheless, numerous studies have shown that bereaved individuals have higher rates of disability and medication use than their nonbereaved counterparts [1] – [7] , and are themselves at heightened risk of death [8] – [11] . The excess morbidity and mortality is likely to be concentrated in a grief-stricken few. The challenge has been to identify vulnerable bereaved individuals so that interventions could reduce their risk of adverse outcomes.

Following a major loss, such as the death of a spouse, a noteworthy minority of bereaved individuals experiences “a clinically significant behavioral or psychological syndrome or pattern that occurs in an individual and that is associated with present distress or disability” [12] . These are the requirements for meeting the definition of a mental disorder in the Diagnostic Statistical Manual of Mental Disorders , 4th Edition ( DSM-IV ) [12] . Nevertheless, the DSM-IV excludes griefterm as a disorder on the grounds that it is “an expectable and culturally sanctioned response to a particular event” [12] . In the DSM-IV , bereavementterm is classified as a “V” code; that is, an “other condition that may be a focus of clinical attentionterm” [12] . Similarly, in the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision ( ICD-10 ) [13] , bereavementterm is classified as a “Z” code, which refers to “occasions when circumstances other than a disease or injury result in an encounter or are recorded by providers as problems or factors that influence care” [14] .

The DSM-IV and ICD-10 focus on the distinction between “normal” griefterm and major depressive disorder (MDD), but neglect to acknowledge that griefterm, per se, may be pathological. Studies have shown that symptoms denoting complicated, or prolonged, griefterm are distinguishable from symptoms of uncomplicated griefterm [15] – [18] and that only the former are associated with significant impairment [15] – [25] . The aim of the present study is to validate criteria for prolonged grief disorderterm·def (PGDterm) proposed for inclusion in DSM-V and ICD-11 . The justification for validating criteria for PGDterm and proposing inclusion in DSM-V and ICD-11 lies in the distinctive phenomenology, etiology, course, response to treatment, and adverse outcomes associated with PGDterm symptoms.

PGD symptomatologyterm—variously referred to as “complicated griefterm” (CG) [15] , [17] – [20] , [22] , [25] – [28] , “traumatic griefterm” (TG) [21] , [23] , [24] , [29] , and complicated griefterm disorder (CGD) [22] —have repeatedly been shown to be different from the symptoms of other DSM-IV and ICD-10 disordersterm (e.g., MDD). For example, in studies of bereaved individuals from a variety of different countries, yearningterm·def loads highly on the griefterm factor, but not on depression or anxiety factors, whereas sadness loads highly only on a depression factor, and feeling nervous and worried loads highly only on an anxiety factor [15] , [19] , [20] , [26] , [28] – [31] . A study of negative cognitions among bereaved individuals found that being overwhelmed by the loss (i.e., “If I would fully realize what the death of ___ meant, I would go crazy”) was a cognition specific to PGDterm, but not depression [32] . The distinction between the symptoms of griefterm and depressive symptoms found in bereaved individuals has also been shown in advanced cancer patients [30] and caregivers of nursing home residents with advanced dementia [31] , [33] .

The set of risk factors and clinical correlates of PGDterm includes a history of childhood separation anxiety [34] , controlling parents [35] , parental abuse or death [36] , a close kinship relationship to the deceased (e.g., parents) [37] , [38] , insecure attachment styles [39] , marital supportiveness and dependency [39] , [40] , and lack of preparation for the death [41] , [42] —all suggesting that attachment issues are salient in creating a vulnerability to PGDterm. For example, we find that feelings of emotional dependency on the dying patient is associated with symptoms of griefterm, but not with symptoms of depression in patient caregivers [39] and recently bereaved persons [40] . We have also found that childhood separation anxiety uniquely predicts PGDterm, but not MDD, posttraumatic stress disorder (PTSD), or generalized anxiety disorder (GAD) following bereavementterm later in life [34] . The identified griefterm symptoms have been shown not to relate to the changes of electroencephalographic (EEG) sleep physiology associated with MDD [43] . Most recently, a functional magnetic resonance imaging (fMRI) study by O'Connor et al. [44] has demonstrated that only patients with complicated griefterm showed reward-related neural activity in the nucleus accumbens in response to reminders of the deceased. The nucleus accumbens cluster “was positively associated with yearningterm·def, but not with time since death, participant age, or positive/negative affect” [44] . Taken together, these findings suggest distinct clinical correlates of griefterm symptoms relative to depressive symptoms.

PGDterm symptoms also demonstrate incremental validity in that they are associated with elevated rates of suicidal ideation and attempts, cancer, immunological dysfunction, hypertension, cardiac events, functional impairments, hospitalization, adverse health behaviors, and reduced quality of life in adults [19] , [21] , [24] , [25] , [30] , [45] and in children and adolescents [46] , after controlling for the effects of depression and/or anxiety. In a Swedish sample of bereaved parents 4–9 y after the death of their child from cancer, parents with unresolved griefterm were at risk for long-term mental and physical impairments, increased health service use, and increased sick leave over and above the effects of depression and anxiety [47] . These findings highlight the enduring nature of bereavement-related distress and disability, and the societal consequences of unresolved griefterm.

The course and response to treatment of PGDterm differ from those of normal griefterm [48] , [49] and depression [48] – [52] . Tricyclic antidepressants alone and with interpersonal psychotherapy have proven ineffective relative to placebo for the reduction of PGDterm symptoms [50] – [52] . By contrast, randomized, controlled trials of psychotherapy designed specifically for PGDterm have demonstrated efficacy for PGDterm symptom reduction [53] , [54] . The efficacy of a PGD-specific treatment highlights the benefits of an accurate diagnosis.

Although the results above suggest that symptoms of griefterm constitute a syndrome that operationally defines a mental disorder, no agreed upon and tested diagnostic algorithm for PGDterm exists. Psychiatrists such as Lindemann [55] , ParkespersName [56] , RaphaelpersName [57] , HorowitzpersName [22] , and JacobspersName [58] have noted the suffering associated with intense and/or chronic mourning. Nevertheless, no explicit criteria developed from a consensus process have been assessed and then tested in a community-based sample of bereaved individuals. The absence of explicit and agreed upon (i.e., standardized) criteria for PGDterm has hampered efforts for its inclusion in the DSM and ICD systems. The establishment of standardized criteria for PGDterm would enable researchers to investigate the prevalence, risk factors, outcomes, neurobiology, prevention, and treatment of this disorder. Such criteria would also assist clinicians in the accurate detection and treatment, as well as reimbursement for treatment, of PGDterm.

As a firstpersName step toward the development of consensus criteria for PGDterm, we convened a group of experts in bereavementterm, mood and anxiety disorders, and psychiatric nosology to review the evidence justifying the development of diagnostic criteria [23] . Following the panel's conclusion that the evidence merited the development of a diagnostic algorithm for a griefterm disorder, they engaged in a 2-d workshop culminating in the formulation of consensus criteria. A preliminary testing of the criteria analyzed the most relevant, yet incomplete, data available at the time—data lacking the full set of proposed consensus criteria and an independent rating to diagnose PGDterm. Results of this preliminary report supported the sensitivity and specificity of the initially proposed algorithm [23] .

Here, we report the results of a field trial designed specifically to develop and evaluate diagnostic algorithms for PGDterm based on symptoms proposed by the consensus panel. The aim of this study was to establish the psychometric validity of, and propose criteria for, a new syndrome, PGDterm.

Methods Sample Data were obtained for the Yale Bereavementterm Study (YBS) (e.g., [25] , [34] – [36] , [40] , [41] , [45] , [48] ), a National Institute of Mental Health (NIMH)-funded (MH56529) investigation to conduct a field trial of consensus criteria [23] for PGDterm. The YBS was a longitudinal, interview-based study of community-dwelling bereaved individuals in Connecticut. The YBS was approved by the institutional review boards (IRBs) of all participating sites and was in accordance with Health Insurance Portability and Accountability Act (HIPAA) regulations.

Recruitment involved locating family survivors bereaved 6 mo or less found on contact lists of the Greater Bridgeport/Fairfield American Association of Retired Persons (AARP) Widowed Persons Service (WPS), a community-based outreach program. The contact lists provided names of recently widowed persons who a volunteer widowed person would contact to describe the WPS program. Fewer than 5% of those contacted participated in any WPS program; the lists included those approached, but not necessarily actively involved in, the WPS. A comparison between vital records and the WPS contact list revealed that WPS listings provide an unbiased and comprehensive ascertainment of recently widowed people. Participants were also recruited from pastoral care offices in the New Haven area. Participants from this alternative source (117/317 = 37.0% of study participants) did not differ significantly from WPS participants (200/317 = 63.0% of study participants) on gender, income, education, race/ethnicity, or quality of life, but they were younger than WPS participants ( p = 0.05) (mean age = 59.7 y, standard deviation [SD] = 16.4 versus 63.2 y, SD = 11.5 y, respectively).

Of the 575 potential participants contacted, 317 (55.1%) agreed to participate. Reasons for nonparticipation included reluctance to participate in research ( n = 11; 4.3%); being too busy ( n = 46; 17.8%) or too upset ( n = 27; 10.5%); “doing fine” ( n = 23; 8.9%); “not interested” or “no reason” ( n = 145; 56.2%); and “other” reasons ( n = 6; 2.3%). Nonparticipants were more likely to be male (37.2% versus 25.9%, p <0.001) and older (mean age = 68.8 y versus 61.7 y, p <0.001) than participants. Written informed consent was obtained from all study participants. Interviews were conducted by master's degree–level interviewers trained by YBS investigators (HGP, SCJ). Interviewers were required to demonstrate nearly perfect agreement (κ≥0.90) with the YBS investigators for diagnoses of psychiatric disorders (e.g., MDD) and PGDterm in five pilot interviews before being permitted to interview for the study.

The 317 YBS participants were interviewed at baseline an average of 6.3 mo (SD = 7.0 mo) post-loss. FirstpersName follow-up interviews ( n = 296, 93.4% of participants) were completed an average of 10.9 mo (SD = 6.1 mo) post-loss; second follow-up interviews ( n = 263, 83.0% of participants) at an average of 19.7 mo (SD = 5.8 mo) post-loss. The average age of participants was 61.8 y (SD = 18.7 y), most were female (73.7%), white (95.3%), educated beyond high school (60.4%), and spouses of the deceased (83.9%). Data were restructured such that assessments were grouped into more uniform post-loss time periods (0–6 mo, 6–12 mo, and 12–24 mo post-loss). A single assessment within each time period was randomly selected for each participant to remove cases in which two assessments occurred within the same interval. The present study sample ( n = 291; 91.8% of YBS participants) included participants interviewed at least once within 12 mo post-loss and who provided sufficient information to evaluate PGDterm.

Assessment of Symptoms of PGDterm Symptoms of PGDterm were assessed with the rater version of the Inventory of Complicated Griefterm—Revised (ICG-R) [34] – [36] , [40] , [41] , [45] , [59] , a structured interview designed to assess a wide variety of potential PGDterm symptoms, using five-point scales to represent increasing levels of symptom severity. The ICG-Rterm is a modification of the Inventory of Complicated Griefterm (ICG) [15] that includes all the symptoms proposed by the consensus panelterm [23] and additional symptoms enabling the testing of alternative diagnostic algorithms [22] . The ICG-Rterm and the original ICG have both proven highly reliable (e.g., [15] , [25] , [36] , [41] ) (e.g., Cronbach's α>0.90; test-retest reliability coefficient = 0.80 [15] ) and to possess criterion validity [15] , [21] , [24] , [25] , [45] . Based on prior work [23] , [59] , a symptom was considered present if rated 4 or 5, and absent if rated 1, 2, or 3, on its five-point scale. Interviewers were trained by project investigators (HGP, SJC) to provide a separate evaluation of whether or not the participant represented a current “case” of PGDterm.

Assessment of Psychiatric Disorders Psychiatric disorders were assessed using the Structured Clinical Interview for DSM-IV (SCID Non-Patient Version) [60] . The rater-administered SCID assessed criteria for DSM-IV anxiety disorders (GAD, PTSD, and panic disorder [PD]) and mood disorders (MDD). Research has supported the reliability and validity of SCID diagnoses [61] .

Assessment of Additional Outcomes Positive responses to one or more of the four Yale Evaluation of Suicidality [25] screening questions were categorized as having suicidal ideation. The Established Populations for Epidemiological Studies of the Elderly [62] measured performance of activities of daily living [63] and physical functioning [64] . Individuals with at least “some difficulty” with at least one of the 14 tasks (e.g., bathing) were considered functionally impaired in order to make the measure sensitive to impairment in a highly functioning sample. Scores less than 5 (below the lowest quartile) on the Medical Outcomes Short-Form [65] indicated inferior quality of life.

Analyses and Results The psychometric validation of diagnostic criteria for PGDterm proceeded through a cumulative series of analyses, with each phase in the overall analysis having a distinct aim. In Phase 1 of the analysis, the aim was to limit the set of candidate symptoms for PGDterm to those that were informative and unbiased. In Phase 2 of the analysis, the goal was to construct an objective, reliable, valid symptom criterion standardterm·def for PGDterm by which to evaluate alternative diagnostic algorithms for meeting symptom criteria for PGDterm. The aim of Phase 3 of the analysis was to identify a specific, optimum diagnostic algorithm for meeting symptom criteria for PGDterm among a large set of candidate algorithms. Phase 4 of the analysis was designed to evaluate the predictive validity for temporal subtypesterm·var of meeting the optimal symptom criteria for PGDterm as an empirical means to inform the specification of a “timing criterion” for the diagnosis of PGDterm. In Phase 5, the goal was to propose a complete set of “ DSM -style” diagnostic criteria based on results of the preceding phases in the analysis. Phase 6 of the analysis evaluated the predictive validity of the final, complete, proposed criteria for PGDterm.

Phase 1: deriving a set of informative, unbiased symptoms of PGDterm IRT [66] , item information function (IIF) analysis, and differential item functioning (DIF)term·var analysis were used to evaluate candidate symptoms for PGDterm assessed 0–12 mo post-loss. IIF analysis was used to evaluate the amount of information about the prolonged griefterm·var (PG) “attribute” (underlying construct) provided by each of 22 dichotomous candidate symptoms for PGDterm. Consistent with the use of IRT to construct a one-dimensional scale for PG, Cattell's scree test [67] indicated that griefterm, as measured by these 22 symptomsterm, is one-dimensional. Figure 1 presents item information functions for these 22 symptomsterm derived from a two-parameter logistic (2-PL) item response model (IRM). Within the framework of IRT, information for a given value of the latent PG attribute is inversely related to its conditional standard error of measurement. Greater information implies lower measurement error, and greater measurement precision, for PG. Six symptoms with maximum “peak” information less than 20% of that of the most informative symptom were considered to be relatively uninformative and removed from further consideration as possible symptoms for assessing and diagnosing PGDterm. DIF analysis of between-group differences in item location parameters was used to evaluate potential biases in the assessment of the remaining 16 informative, candidate symptoms for PGDterm with respect to age (less than 65 y versus greater than or equal to 65 y), gender (male versus female), education (beyond versus not beyond high school), relationship to the deceased (spouse versus nonspouse), and time from loss (0–6 versus 6–12 mo post-loss). Figure 2 displays item characteristic curves by group, spouse, and nonspouse, for two items eliminated from consideration as possible symptoms for assessing and diagnosing PGDterm due to evidence of DIF using a 16-item 2-PL IRM. A total of four of 16 informative symptoms were found to be biased with respect to time from loss, gender, and/or relationship to the deceased. Table 1 provides a summary of results for these IRT IIF and DIF analyses of candidate symptoms for assessing and diagnosing PGDterm.

Figure 1 Relative item information as a function of the prolonged griefterm·var attribute for 22 candidate symptoms for PGDterm.

IRT IIF analysis of 22 binary candidate symptoms for PGDterm was performed using a 2-PL IRM. This figure displays item information as a function of the PG attribute for all 22 of these symptoms included in this IRM, relative to the maximum information for the most informative symptom, “inability to care about others since the death.” The horizontal line in the figure represents the standard used to discriminate between 16 informative candidate symptoms retained for further analysis, and six uninformative candidate symptoms excluded from further analysis (as indicated in Table 1 ).

Figure 2 Differential item functioning for two biased symptoms.

IRT DIF analysis of candidate symptoms for PGDterm was performed with respect to age (less than 65 y versus greater than or equal to 65 y), gender (male versus female), education (beyond versus not beyond high school), relationship to the deceased (spouse versus nonspouse), and time from loss (0–6 mo versus 6–12 mo post-loss). This figure displays IRT item characteristic curves (ICCs) for two symptoms found to differ with respect to relationship to the deceased (spouse versus nonspouse). The horizontal error bar associated with each ICC represents the standard error in the estimate of the location of the ICC with respect to the PG attribute. Of 16 informative symptoms examined, four symptoms displayed DIF and were excluded from further analysis (as indicated in Table 1 ).

Table 1 Evaluation of candidate symptoms for PGDterm ( n = 287).

Candidate PGDterm Symptom Rate (%) IRT IIF Analysis a IRT DIF Analysis b I max c Θ max d Sex Spouse Time Inability to care about others since the death 6.6 1.00 1.70 Biased Yearningterm·def for, or preoccupation with, deceased 68.3 0.94 −0.53 Life empty, meaningless without deceased 34.8 0.93 0.46 Stunned, dazed, or shocked about the death 19.2 0.58 1.07 Trouble accepting the death 32.7 0.56 0.56 Feel part of you died along with the deceased 37.6 0.49 0.41 Difficulty moving on with life without deceased 18.1 0.46 1.17 Sense of numbness since the death 13.6 0.46 1.41 Future holds no meaning without the deceased 14.6 0.38 1.40 Biased Hard for you to trust others since the death 7.0 0.36 2.00 Avoid reminders of deceased 12.5 0.26 1.67 Survivor guilt 8.4 0.25 2.04 Loneliness as a result of the death 57.1 0.24 −0.26 Biased Biased Biased Lost sense of security since the death 23.3 0.23 1.09 Biased Bitterness or anger related to the death 25.1 0.23 1.01 On edge, jumpy since the death 11.5 0.20 1.88 Envious of others who have not lost someone close 7.0 0.16 2.51 Memories of the deceased upset you 22.6 0.14 1.31 Drawn to places, things associated with deceased 31.0 0.14 0.86 Disturbed sleep since the death 23.3 0.13 1.28 The death has shattered your world view 28.6 0.13 1.02 Lost sense of control since the death 16.4 0.10 1.93 Relatively uninformative ( I max <0.20) or biased symptoms are displayed in bold font . All others are informative, unbiased symptoms and were retained for further analysis.

a IRT IIF analysis was performed using all 22 symptoms, showing 16 to be informative ( I max ≥0.20).

b IRT DIF analysis was restricted to 16 relatively informative symptoms, showing four to be biased.

c I max represents maximum item information relative to that of “inability to care about others….”

d Θ max represents location of I max for the item along the PG attribute scale.

The following 12 informative, unbiased ICG-R symptoms were retained for consideration in a diagnostic algorithm: yearningterm·def; avoidance of reminders of the deceased; disbelief or trouble accepting the death; a perception that life is empty or meaningless without the deceased; bitterness or anger; emotional numbness or detachment from others; feeling stunned, dazed or shocked; feeling part of oneself died along with the deceased; difficulty trusting others; difficulty moving on with life; on edge or jumpy; survivor guilt (Cronbach's α = 0.82).

Phase 2: deriving a criterion standardterm·def for assessing diagnostic algorithms for symptoms of PGDterm In the absence of an established, standard method for diagnosing PGDterm, there was a need to develop a criterion standardterm·def for “caseness” of PGDterm by which the performance of alternative algorithms for PGDterm could be evaluated. As a potential criterion standardterm·def for PGDterm, the rater determination of caseness of PGDterm had the advantage of reflecting experienced clinical judgment. However, rater assessments of PGDterm were subjective, were made without explicit reference to any established criteria, and were not always consistent with more objective, reliable assessments of PG as measured with IRM scores for the underlying PG attribute (i.e., raters assign PGDterm to some individuals with low scores, and not to others with high scores, on the PG attribute scale). It was decided that a criterion standardterm·def for caseness should be informed by clinical judgment, but should also be a function of PG symptom severity. Dichotomized IRM PG attribute scores, informed by rater assessments of PGDterm, would provide objective, reliable, valid criterion standardterm·def diagnoses for PGDterm.

Scores from a 2-PL IRM for PG based on the 12 informative, unbiased symptoms were used to order individuals in terms of PG symptom severity. Agreement between rater and minimum-threshold PG attribute assessments of caseness of PGDterm was maximized to establish an optimum minimum threshold for caseness of PGDterm along this IRM scale. As illustrated in Figure 3 , PGDterm “cases” determined by a minimum-threshold “cutoff” PG attribute score of approximately 1.0 had the greatest agreement (κ = 0.68) with cases determined by the rater assessments. An IRM PG attribute score above this minimum-threshold cutoff value became our criterion standardterm·def for PGDterm caseness.

Figure 3 Agreement between rater diagnoses and dichotomized prolonged griefterm·var attribute score diagnoses of PGDterm as a function of cutoff PG attribute score for diagnosis.

Dichotomized IRM PG attribute scores provide objective, reliable criterion standardterm·def diagnoses for PGDterm. This figure illustrates how rater diagnoses were used to establish a minimum-threshold cutoff PG attribute score for diagnosis of PGDterm (i.e., PG attribute score≥minimum-threshold cutoff PG attribute score). An optimal cutoff PG attribute score of 1 maximized agreement between rater diagnoses and dichotomized IRM PG attribute score diagnoses of PGDterm.

Phase 3: identifying an optimal diagnostic algorithm for symptoms of PGDterm Based on consensus opinion of the previously mentioned expert panel [23] , and confirmed by results showing yearningterm·def was the most common (68.3%) and most informative ( I max = 0.94) of the 12 items and provided the maximum information and the lowest degree of severity (Θ max = −0.53), yearningterm·def was specified as a mandatory symptom. The analyses then sought to determine the number and combination of the remaining 11 (nonmandatory) symptoms in addition to yearningterm·def that would yield the most efficient (i.e., optimum balance between sensitive and specific) diagnosis for PGDterm with respect to our criterion standardterm·def. Combinatorics [68] , the branch of mathematics that studies the number of different ways of arranging sets, was used to enumerate alternative sets of nonmandatory symptoms to construct alternative, candidate diagnostic algorithms for meeting the symptom criterion for PGDterm. Each of these diagnostic algorithms was specified in terms one common, mandatory symptom, yearningterm·def, a specific set of n other, nonmandatory symptoms, and some minimum number of nonmandatory symptoms within this set, k , which one must have to satisfy the symptom criterion for PGDterm. A total of 4,785 of these algorithms for meeting the symptom criterion for PGDterm were enumerated [i.e., the sum of (11 choose n ×( n −3) for n = 5, 6, 7, 8, 9, where (11 choose n ) represents the number of ways of choosing n of 11 nonmandatory symptoms, n ∈ {5, 6, 7, 8, 9}, and ( n −3) represents the number of values of k ∈ {3, …, n −1}, considered for a given value of n ] and subsequently evaluated with respect to the criterion standardterm·def. Algorithms requiring yearningterm·def and as few as three of five, and as many as eight of nine, additional symptoms were considered.

Figure 4 displays results for a subset of the diagnostic algorithms considered. Each data point in Figure 4 represents the sensitivity and specificity of a unique diagnostic algorithm. The optimal, most efficient algorithm included yearningterm·def and at least five of the nine following symptoms: avoidance of reminders of the deceased; disbelief or trouble accepting the death; a perception that life is empty or meaningless without the deceased; bitterness or anger related to the loss; emotional numbness; feeling stunned, dazed, or shocked; feeling part of oneself had died along with the deceased; difficulty trusting others; difficulty moving on with life (sensitivity = 1.00; specificity = 0.99; positive predictive value = 0.94; negative predictive value = 1.00). The optimal algorithm displayed convergent validity with respect to the previously proposed diagnostic algorithm for PGDterm (κ = 0.68) and the rater diagnosis of PGDterm (κ = 0.68), and discriminant validity with respect to other mood and anxiety disorders (Φwith MDD = 0.36; PTSD = 0.31; GAD = 0.17).

Figure 4 Alternative diagnostic algorithms for meeting symptom criteria for PGDterm.

Each data point in this figure represents the performance, in terms of sensitivity and specificity with respect to a criterion standardterm·def for PGDterm, of a unique “ DSM -style” diagnostic algorithm for meeting symptom criteria for PGDterm. Each algorithm is specified in terms of one common, mandatory symptom, yearningterm·def, a specific set of n other, nonmandatory symptoms, and some minimum number of nonmandatory symptoms within this set, k , which one must have to satisfy the symptom criterion for PGDterm. Based on the current data, the optimal, most efficient algorithm requires having yearningterm·def and at least five of the following nine symptoms: avoidance of reminders of the deceased; trouble accepting the death; a perception that life is empty or meaningless without the deceased; bitterness or anger related to the loss; emotional numbness; feeling stunned, dazed or shocked; feeling that part of oneself died along with the deceased; difficulty in trusting others; and difficulty moving on with life.

Phase 4: evaluating the predictive validity for temporal subtypesterm·var of PGDterm Three subtypes of PGDterm were defined in terms of patterns of meeting diagnostic criteria for PGDterm at 0–6 and 6–12 mo post-loss: acute = meeting the symptom criteria for PGDterm at 0–6 mo, but not at 6–12 mo, post-loss; delayed = meeting the symptom criteria for PGDterm at 6–12 mo, but not at 0–6 mo, post-loss; and persistent = meeting the symptom criteria for PGDterm both at 0–6 and at 6–12 mo post-loss. In Table 2 , we see that the acute temporal specification was not significantly associated with any of the examined outcomes evaluated 12–24 mo post-loss. Delayed was significantly ( p <0.001) associated with suicidal ideation and poor quality of life. Persistent was significantly ( p <0.01) associated with mental disorders (MDD, PTSD, or GAD), suicidal ideation, and poor quality of life. Delayed or persistent was significantly ( p <0.05) associated with psychiatric disorders (MDD, PTSD, or GAD), suicidal ideation, functional disability, and poor quality of life. These results indicate that diagnoses of PGD before 6 mo post-lossterm do not effectively identify bereaved individuals at risk of long-term dysfunction, whereas delayed and persistent temporal subtypesterm do.

Table 2 Mental health and functional consequences of meeting symptom criteria for PGDterm by temporal subtypeterm·var.

Outcome (12–24 Mo Post-Loss) Relative Risk for Outcome Associated with PGDterm Temporal Subtypeterm·var: Acute (15/172 [8.7%]) a Delayed (6/172 [3.5%]) a Persistent (12/172 [7.0%]) a Delayed or persistent (28/242 [11.6%]) b RR 95% CI RR 95% CI RR 95% CI RR 95% CI MDD, PTSD, or GAD 1.54 (0.20–11.98) 3.86 (0.55–27.22) 11.58*** (4.41–30.43) 10.19*** (4.72–21.99) Suicidal ideation ( n = 171:241) c 1.97 (0.64–6.09) 4.93*** (1.92–12.64) 3.29* (1.28–8.43) 4.44*** (2.62–7.53) Functional disability ( n = 170:240) c 0.51 (0.18–1.45) 1.54 (0.73–3.25) 1.40 (0.79–2.50) 1.65** (1.16–2.34) Poor quality of life ( n = 168:238) c 0.76 (0.20–2.89) 3.78*** (1.93–7.40) 2.58* (1.23–5.41) 3.17*** (2.03–4.95) Acute = meeting symptom criteria at 0–6 mo, but not at 6–12 mo, post-loss; Delayed = not meeting symptom criteria at 0–6 mo, but meeting symptom criteria at 6–12 mo post-loss; Persistent = meeting symptom criteria at 0–6 and 6–12 mo post-loss.

a The denominator included those assessed at both 0–6 and 6–12 mo post-loss.

b The denominator included all those assessed at 6–12 mo post-loss, regardless of the 0–6-mo post-loss assessment.

c Sample sizes ( n ) varied due to missing data. The firstpersName number in the parenthesis represents n for those assessed at both 0–6 and 6–12 mo post-loss, the second number after the colon represents n for those assessed at 6–12 mo post-loss regardless of the 0–6-mo post-loss assessment.

* p <0.05; ** p <0.01; *** p <0.001.

CI, confidence interval; RR, relative risk.

Phase 5: proposing criteria for PGDterm To reduce further the likelihood of a false-positive diagnosis, a timing criterion (Criterion D) was added to specify that a diagnosis not be made until at least 6 mo have elapsed since the death. This would exclude the acute cases described above in which a person with initially high levels of griefterm in the firstpersName few months experiences declines in griefterm intensity at and beyond 6 mo post-loss. To be conservative in our diagnosis of PGDterm, we also added a requirement that the symptomatic distress be associated with functional impairment (Criterion E).

The ultimate consensus criteria set for PGDterm proposed for DSM-V and ICD-11 appears in Table 3 . Diagnoses of PDG based on these criteria demonstrated convergent validity with respect to the diagnostic algorithm proposed by HorowitzpersName et al. [22] (κ = 0.69) and the rater diagnosis of PGDterm (κ = 0.52), and discriminant validity with respect to other mood and anxiety disorders (Φ with MDD = 0.48; PTSD = 0.23; GAD = 0.21).

Table 3 Criteria for PGDterm proposed for DSM-V and ICD-11 .

Category Definition A. Event : Bereavementterm (loss of a significant other) B. Separation distress : The bereaved person experiences yearningterm·def (e.g., craving, pining, or longing for the deceased; physical or emotional suffering as a result of the desired, but unfulfilled, reunion with the deceased) daily or to a disabling degree.

C. Cognitive, emotional, and behavioral symptoms : The bereaved person must have five (or more) of the following symptoms experienced daily or to a disabling degree: 1. Confusion about one’s role in life or diminished sense of self (i.e., feeling that a part of oneself has died) 2. Difficulty accepting the loss 3. Avoidance of reminders of the reality of the loss 4. Inability to trust others since the loss 5. Bitterness or anger related to the loss 6. Difficulty moving on with life (e.g., making new friends, pursuing interests) 7. Numbness (absence of emotion) since the loss 8. Feeling that life is unfulfilling, empty, or meaningless since the loss 9. Feeling stunned, dazed or shocked by the loss D. Timing : Diagnosis should not be made until at least six months have elapsed since the death.

E. Impairment : The disturbanceterm causes clinically significant impairmentterm in social, occupational, or other important areas of functioning (e.g., domestic responsibilities).

F. Relation to other mental disorders : The disturbanceterm is not better accounted for by major depressive disorder, generalized anxiety disorder, or posttraumatic stress disorder.

Phase 6: evaluating the predictive validity of the proposed criteria for PGDterm Among those not concurrently meeting DSM criteria for MDD, PTSD, or GAD ( n = 215), PGDterm diagnoses assessed 6–12 mo post-loss (7/215 = 3.3%) were significantly ( p <0.01) associated with psychiatric diagnoses (MDD, PTSD, or GAD), suicidal ideation, functional disability, and low quality of life 12–24 mo post-loss (see Table 4 ). Among those concurrently meeting DSM criteria for MDD, PTSD, or GAD ( n = 27), PGDterm diagnoses 6–12 mo post-loss (10/27 = 37.0%) were significantly associated with psychiatric diagnoses (MDD, PTSD, or GAD) at 12–24 mo post-loss (relative risk = 2.38, p = 0.043).

Table 4 Mental health and functional impairment at 12–24 mo post-loss associated with PGDterm among those not meeting DSM criteria for MDD, PTSD, or GAD at 6–12 mo post-loss ( n = 215).

Outcome (12–24 Mo Post-Loss) PGDterm Diagnosis (6–12 Mo Post-Loss) Yes (3.3%) No (96.7%) RR 95% CI MDD, PTSD, or GAD 28.6% 3.4% 8.49** (2.14–33.72) Suicidal ideation a ( n = 214) 57.1% 10.1% 5.63*** (2.64–12.03) Functional disability a ( n = 213) 71.4% 35.9% 1.99** (1.20–3.29) Poor quality of life a ( n = 210) 83.3% 14.7% 5.67*** (3.48–9.22) a Sample sizes ( n ) varied due to missing data.

* p <0.05; ** p <0.01; *** p <0.001.

CI, confidence interval; RR, relative risk.

Discussion Our results indicate that PGDterm meets DSM criteria for inclusion as a distinct mental disorder on the grounds that it is a clinically significant form of psychological distressterm associated with substantial disability. Findings from this field trial of consensus criteria for PGDterm confirm prior work demonstrating the distinctiveness of the symptoms of PGDterm (e.g., [15] , [18] – [20] , [22] , [26] , [27] , [29] – [31] ). The proposed diagnostic algorithm for PGDterm has quite incomplete overlap with established mental disorders commonly occurring among recently bereaved individuals (MDD, PTSD). Further, our results indicate that in the absence of mental disorders found in DSM-IV (e.g., MDD), the proposed algorithm for PGDterm predicts substantial dysfunction—impairment missed by the current psychiatric diagnostic system. Because standard treatments for depression have not always proven effective for the reduction of PGDterm [49] – [52] , whereas psychotherapies designed specifically to ameliorate symptoms of PGDterm have demonstrated efficacy [53] , [54] , there exists a need for the accurate detection and specialized treatment of PGDterm.

Although the YBS data may appear unrepresentative of the general US population, a comparison with US Census 2005 [48] , [69] , [70] data reveals similarities with the US widowed population. For example, the YBS sample was 73.7% female compared with 80.7% of the US widowed population and 95.3% white compared with 80.2% of the US widowed population. Like the population of US widowed individuals, the YBS sample is disproportionately female, white, and elderly. Compared with the US widowed population, however, the study participants were somewhat younger, more likely to be male, and a higher proportion was white and better educated. Future research should replicate the analyses in older, nonwhite, less-educated widowed samples.

Although there is a need to confirm the results in nonwidowed bereaved persons, we consider widowhood following an older spouse's death from natural causes to be the prototypical case of bereavementterm. In the US, 84% of all deaths occur among individuals who are 65 y and over [71] , and less than 7% of deaths are from unnatural causes (e.g., unintentional injuries, assault, suicide) [72] . Given that in later life one's spouse/partner is the person most likely to be adversely affected by the death, a sample of older widowed persons surviving the death of a spouse from natural causes provides an important sample in which to develop and test criteria for a bereavement-related mental disorder. In addition, the symptoms retained were only those proven to be invariant across gender, time from loss, and kinship groups (e.g., IRT DIF analysis removed items that performed differently based on whether or not the deceased was a spouse) and a distinct advantage of IRT is that it produces generalizable results regardless of sample characteristics [66] . Thus, the results are expected to be generalizable to most bereaved individuals. The generalizability of the results reported here is not intended to deny the value in further confirmation of the findings in nonwidowed, more traumatically bereaved, younger, less-educated, more male, and ethnically and geographically diverse samples, and the need to examine longer-term bereavementterm outcomes (e.g., 3, 5, and 10 y post-loss).

Although the sample size may appear modest, the study was designed and appropriately powered to evaluate a wide range of potential diagnostic criteria (i.e., the firstpersName phases of the analyses used the full sample [ n = 291]). The YBS PGDterm prevalence rate was obtained in a resilient community sample in which rates of mental illness were lower than those that have been reported in other bereavementterm studies (e.g., 9% for MDD compared with 22% in the firstpersName year of widowhood) [73] . The only analyses limited by statistical power would have been the predictive validity analyses. Here, we found large, statistically significant effects suggesting the conservative nature of our estimates of functional impairment associated with PGDterm.

Study participants may have been less distressed than study nonparticipants. Given the relatively low rates of MDD in the YBS sample and that 10.5% refused participation in the YBS due to being “too upset,” the prevalence rate of PGDterm reported here may be an underestimate. In addition, our statistical power to detect significant effects of PGDterm on mental health and functional impairment outcomes would be lower than would have been the case if more distressed nonparticipants with PGDterm had been included in the study sample.

Conclusion This report provides psychometric validation of a diagnostic algorithm for PGDterm. Although further validation work will, no doubt, be needed, we consider the evidence sufficient to justify PGDterm's serious consideration for inclusion in DSM-V and ICD-11 . In light of the recent concerns about financial conflicts of interest in psychiatric research, especially that which involves pharmaceutical manufacturers, it is noteworthy that this study was federally funded by the US NIMH, and no part of this research was sponsored by producers of a potential therapeutic remedy for PGDterm.

Although most bereaved individuals will eventually adapt to the loss of a significant other more or less successfully, a significant, identifiable minority will experience chronic and disabling griefterm. A PGDterm diagnosis has the potential to enhance the detection and effective treatment of a substantial cause of morbidity among persons who have experienced the loss of a significant other. The diagnosis and treatment of PGDterm offers the promise of reducing the personal and societal toll taken by prolonged griefterm·var.

Abbreviations 2-PL two-parameter logistic DIF differential item functioning DSM-IV Diagnostic Statistical Manual of Mental Disorders , 4th Edition GAD generalized anxiety disorder ICD-10 International Statistical Classification of Diseases and Related Health Problems ICG-R Inventory of Complicated Griefterm—Revised IIF item information function IRM item response model IRT item response theory MDD major depressive disorder PG prolonged griefterm·var PGDterm prolonged grief disorderterm·def PTSD posttraumatic stress disorder SCID Structured Clinical Interview for DSM-IV WPS Widowed Persons Service YBS Yale Bereavementterm Study Footnotes MBF received consultant fees over the past 5 years from Roche, Corcept, Wyeth, Cephalon, Astra-Zeneca, Shire, GSK, and Eli Lilly for preparing diagnostic interviews and/or conducting diagnostic trainings at investigator meetings.

HGP was supported by National Institute of Mental Health grants MH56529 and MH63892, and National Cancer Institute grant CA106370. PKM was supported by NIH grant NS044316. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.