Several noteworthy substance-specific results were obtained, as shown in Table 4. For the reader’s reference, genetic and environmental effects for each substance were calculated as follows using smoking at age 16–17 as an example: total common genetic effects were determined by multiplying the factor loading for this age (0.70) by the common genetic estimates for this age (0.87 and 0.21), provided in Table 3, squaring these results, and then adding them [(0.70× 0.87)2+(0.70×0.21)2]. Residual smoking-specific genetic and environmental effects were determined by squaring the residual estimates provided in Table 4. Smoking-specific genetic effects at age 16–17 were calculated as [(−0.012)+(0.332)]. Adding the results of these two calculations provided the total genetic/environmental effects for the substance.
