The incidence rate represents the new onset of low back pain within the study population per 1,000 personyears. Unadjusted incidence rates of low back pain among military vehicle operators and nonvehicle operators were initially calculated with regard to the following demographic variables: sex, race, age, rank, service, and marital status. Multivariate Poisson regression analysis was used to adjust the incidence rate ratios (IRRs) for other variables in the model. Adjusted IRRs were calculated within each group against a referent, the subgroup with the lowest unadjusted incidence of low back pain among military vehicle operators. SAS software version 9.1 (SAS Institute, Inc., Cary, NC, USA) was used to perform all statistical analyses