Assessment of depression in veterans across missions: a validity study using Rasch measurement models

Abstract

Background: Depression is a common psychopathological outcome following military deployment. Previous studies have reported differing rates of post-deployment depression, indicating that the toll of war differs across missions. However, it is unclear to what degree the varying prevalence is due methodological differences. Studies comparing rates of depression across cohorts using the same methodology and ensuring measurement invariance are rare, leaving us with limited knowledge on the actual depression prevalence variance across missions. Objective: Applying Rasch models (RM), we aim to validate a measure of depression distributed to all personnel deployed with the Danish Defense since 1998. The main focus was establishing a sufficient sum score and measurement invariance relative to deployment cohort. Method: Two cohorts of the International Security Assistance Force (ISAF) deployed to Afghanistan in 2009 (ISAF7, N = 265) and 2013 (ISAF15, N = 271) were included. Participants filled out a questionnaire concerning their Psychological Reactions to International Missions (PRIM) approximately seven months after home-coming. The questionnaire included a 10-item scale of depression symptoms (PRIM-Depression). The validity of the PRIM-Depression was tested using RM with specific focus on differential item functioning (DIF) across the two cohorts. Results: The PRIM-Depression scale displayed excellent overall consistency and showed no problems with monotonicity or homogeneity. However, the full PRIM-Depression scale did not fit a pure RM. We therefore tested the fit of items to a graphical log-linear RM and found evidence of DIF for two items relative to cohort. We proceeded without these two items and tested the resulting 8-item version which fitted a pure RM without DIF on any of the exogenous variables. Conclusions: Our results suggest that the 10-item PRIM-Depression scale should be used to compare cohorts only with appropriate score equation. The 8-item version provides a sufficient statistic and can as such be applied using the raw score.

Perceived danger during deployment: a Rasch validation of an instrument assessing perceived combat exposure and the witnessing of combat consequences in a war zone

“…These specific cohorts were selected since they, in parallel with PRIM, also provided data on validated questionnaires that can be used for evaluation of criterion validity and the cohorts have previously been used in other validity studies (Karstoft, Nielsen, et al, 2017; Karstoft, Andersen, et al, 2017). Furthermore, while both cohorts deployed to Afghanistan, they did so at different times with very different threat assessments and combat intensity.…”

“…Recently, scales assessing symptoms of PTSD (Karstoft, Andersen, & Nielsen, 2017) and depression (Karstoft, Nielsen, & Nielsen, 2017) from PRIM have been validated to enable the comparison of symptom burden across missions and cohorts. Hence, a thorough validation of a perceived danger scale is of great importance and will enable not only the comparison of stressful experiences during deployment across cohorts and missions, but also of how such experiences relate to post-deployment symptoms of PTSD and depression.…”

Low-level cognitive ability in young adulthood and other risk factors of depression in an observational cohort study among deployed Danish soldiers

“…As an example, the addition of perceived war-zone stress to model 1 had little effect on the OR estimates (including PTSD) in model 2. The outcome measure in this study, the PRIMdepression scale in an eight-item version, has been shown to provide a valid tool for comparing levels of depression for deployments that differ in level of threat and combat exposure [24]. The approximately 65% response rate for the questionnaire data left open the possibility of response bias.…”

“…The PRIM-depression scale consists of ten items addressing different symptoms of depression. The measure has been validated using Rasch models (RM) [24], and an eight-item version of the PRIM-depression scale fitted a pure RM without any differential item functioning. Thus, the eight-item PRIM-depression total score provides a sufficient statistic, and the raw score can be applied as a measure of depression [24].…”

“…The measure has been validated using Rasch models (RM) [24], and an eight-item version of the PRIM-depression scale fitted a pure RM without any differential item functioning. Thus, the eight-item PRIM-depression total score provides a sufficient statistic, and the raw score can be applied as a measure of depression [24]. To establish cut-off scores for the eight-item PRIMdepression scale for categorizing individuals with high levels of depression symptomatology, we conducted a Receiver Operating Characteristics (ROC) Curve analysis (see Supplementary material).…”