A log-linear analysis was used to assess the significance of multiple substance repeated-use or non-use compared to expectations based on the prevalence for each substance independently. For example, based on the Wave 2 prevalence of repeated alcohol use (65.73%), repeated tobacco use (20.50%), and repeated marijuana use (33.45%), we would expect the prevalence of using all three substances to be 4.51% (i.e., 0.6573×0.2050×0.3345×100) and the expected prevalence of repeatedly using only alcohol to be 34.78% (i.e., 0.6573×(1−0.2050)×(1−0.3345)×100) if the risk for use for each substance was independent of the use of another substance. At each wave, the observed prevalence of the lifetime repeated-use of all three substances exceeded expectations. At Wave 1, 4.86% of the sample reported repeatedly using all three substances at some point in their lifetime, compared to the expected prevalence of 0.17%. This observation provided evidence of a general tendency to repeatedly use all three substances. By Wave 2, the prevalence of repeated-use of all three substances had increased to 15.45%. Similarly, the observed prevalence of non-repeated-use of all three substances at each wave (Wave 1, 75.29%;
