Evaluating Prolonged Grief Disorder Symptoms

IRT [66] , item information function (IIF) analysis, and differential item functioning (DIF) analysis were used to evaluate candidate symptoms for PGD assessed 0–12 mo post-loss. IIF analysis was used to evaluate the amount of information about the prolonged grief (PG) “attribute” (underlying construct) provided by each of 22 dichotomous candidate symptoms for PGD. Consistent with the use of IRT to construct a one-dimensional scale for PG, Cattell's scree test [67] (link) indicated that grief, as measured by these 22 symptoms, is one-dimensional. Figure 1 presents item information functions for these 22 symptoms 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 PGD. 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 PGD 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 PGD 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 PGD.
The following 12 informative, unbiased ICG-R symptoms were retained for consideration in a diagnostic algorithm: yearning; 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).