I was hoping you could recommend literature that could help me explain a significant association between the random slope "syx," which is No. of Drinks regressed on no. of treatment sessions, regressed on a perceived stress scale score. I studied the handouts for Topic 12, part 3, but the "syx" in the two-level time series analysis example was not significantly associated with either covariate, female or age. I was hoping to see an explanation where such a relationship is significant. For example, does this mean there is a significant interaction between perceived stress and no. of treatment sessions in predicting no. of drinks?