B – 94 Identification of a Subgroup of Veterans Across Service Eras with High Combat Profiles and Worse Cognitive Outcomes in Million Veteran Program (MVP) Veterans

Abstract Objective Deployed, combat-exposed Veterans experience worse cognitive symptoms compared to non-deployed Veterans. Combat experience has changed over time and variations in cognitive outcomes by military service era are poorly documented. In a nationally representative sample of Veterans, we examined the association of combat experiences with subjective cognition across service eras. Method Participants included 126,841 combat-exposed Veterans enrolled in the Million Veteran Program (MVP) who served “Before” (n=12,188), “During” (n=74,549), or “After” (n=40,104) the Vietnam War. Combat experiences and cognitive symptoms were evaluated using the Combat Experiences Scale (CES) from the Deployment Risk & Resilience Inventory (DRRI) and the Medical Outcomes Study Cognitive Functioning Scale-Revised, respectively. Results Using unbiased dimensionality reduction with k-means clustering, we identified five subgroups of Veterans based on combat experiences; one subgroup (n=44,469; 35%) had high scores across all DRRI questions (i.e., the “high-combat” group) and were represented in all service eras (Before: 27%; During: 41%; After: 26%). Separate generalized linear models adjusted for age, race, ethnicity, and TBI history showed Veterans in the high-combat group had worse cognitive symptoms compared to all other combat groups, with effect sizes increasing with service era recency (Before: beta=0.95; During: beta=1.25; After: beta=2.43; p<.001). Conclusion Higher levels of combat experiences were associated with worse cognitive symptoms, regardless of service era, with the largest effects on post-Vietnam War Veterans. Our findings support the utility of the DRRI-CES screening for Veterans with higher cognitive symptom burden. Future studies will further characterize the high-combat group using other data including genetics.