However, the healthy soldier effect does, for most conditions, diminish with duration of follow-up.
Further work should include the selection a serving, but non-deployed, comparison group, which will reduce the healthy soldier effect.
The use of this comparison group allowed for avoidance of the "healthy soldier effect," which is a selection effect analogous to the "healthy worker effect".
The 'healthy soldier' effect often confounds the interpretation of military cohort studies, but the effect decreases with time, seen here for many causes of morbidity.
A comparison military population may enable considerable control of the healthy soldier effect, but this too may need to be carefully selected.
There was no overall increase in mortality when comparing these two groups, and both groups of veterans showed the healthy soldier effect in SMR analyses.
Interpretation of the results requires consideration of bias in terms of the healthy worker effect, in this case the 'healthy soldier effect.' 6 The application and selection process for military service, and further selection prior to operational deployment, results in a cohort which has lower disease incidence and mortality than the general population.
For example, the increase in SHRs for COPD may be due to a 'catching up' phase from a greater past prevalence of smoking, may be due to an environmental exposure associated with service, or may simply reflect the healthy soldier effect.
The pattern of mortality and cancer incidence is not at odds with the list of compensable conditions and consistent with that found in Australian veterans serving in the same area of Vietnam, but also consistent with smoking and the healthy soldier effect.
The main points of comparison between the two are a similar healthy soldier effect, with significantly fewer deaths from all causes in both cohorts but a contrast in the 6% significant excess of all cancer deaths in the Australian cohort, cancer also being the single most common cause of death.
