Risk ratios and 95% confidence intervals were computed by simulating the change in risk of principal drinking when contact contemporaneous drinking changes from 0 to 1, using 1,000 randomly drawn sets of estimates from the coefficient covariance matrix and assuming all other variables were held at their means.(30) All these tests are two-tailed. For repeated tests involving different types of social contacts we applied a Bonferroni correction to the confidence intervals.
