Power analysis is a key component for planning prospective studies such as clinical trials. However, some journals in biomedical and psychosocial sciences ask for power analysis for data already collected and analysed before accepting manuscripts for publication. In this report, post hoc power analysis for retrospective studies is examined and the informativeness of understanding the power for detecting significant effects of the results analysed, using the same data on which the power analysis is based, is scrutinised. Monte Carlo simulation is used to investigate the performance of posthoc power analysis.

Recent reports suggest US military service members who deployed in support of the recent conflicts in Iraq and Afghanistan have higher rates of new-onset asthma than those who did not deploy. However, it is unknown whether combat experiences, in addition to deployment, contribute to new-onset asthma risk. This study aimed to longitudinally determine the risk factors for developing asthma, including combat deployment (categorized as deployed with combat experience, deployed without combat experience, or nondeployed), among participants in the Millennium Cohort Study from 2001 to 2013. A total of 75,770 participants completed a baseline survey and at least 1 triennial follow-up survey on deployment experiences, lifestyle characteristics, and health outcomes. Complementary log-log models stratified by sex were used to estimate the relative risk of developing asthma among participants who reported no history of asthma at baseline. In models with adjustments, those who deployed with combat experience were 24%–30% more likely to develop asthma than those who did not deploy. Deployed personnel without combat experience were not at a higher risk for new-onset asthma compared with nondeployers. Further research is needed to identify specific features of combat that are associated with greater asthma risk to inform prevention strategies.

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In the first known longitudinal study of the topic, we examined whether experiencing sexual assault or sexual harassment while in the military was associated with increased risk for subsequent unhealthy alcohol use and smoking among U.S. service members in the Millennium Cohort Study (2001-2012). Adjusted complementary log-log models were fit to estimate the relative risk of (a) smoking relapse among former smokers (men: n = 4,610; women: n = 1,453); (b) initiation of unhealthy alcohol use (problem drinking and/or drinking over recommended limits) among those with no known history of unhealthy alcohol use (men: n = 8,459; women: n = 4,816); and (c) relapse among those previously reporting unhealthy alcohol use (men: n = 3,487; women: n = 1,318). Men who reported experiencing sexual assault while in the military had sixfold higher risk for smoking relapse: relative risk (RR) = 6.62; 95% confidence interval (CI) [2.34, 18.73], than men who did not. Women who reported experiencing sexual assault while in the military had almost twice the risk for alcohol relapse: RR = 1.73; 95% CI [1.06, 2.83]. There were no other significant associations. These findings suggest that men and women may respond differently following sexual trauma, and support future concerted policy efforts by military leadership to prevent, detect, and intervene on sexual assault.