Chronbach’s alpha for REX was calculated with the alpha function in the psych R package to test the internal consistency of the 5 items which make up the re-experiencing cluster. Chronbach’s alpha for the 5 reexperiencing items was 0.94 in EAs and 0.95 in AAs. Based on the population definition results, there were initially ~247,000 EA and ~60,000 AA subjects. After accounting for missing phenotype data as only subjects who completed the voluntary surveys could be included, the final sample sizes were 146,660 EAs and 19,983 AAs. Of 146,660 EA subjects, 41.3% were combat-exposed; and of 19,983 AA subjects, 36.2% were combat exposed (extended demographic information, Table S2).
