An intuitive way to examine telescoping is to construct an index of normative progression through milestones, by taking the pairwise interval (difference score) between ages at which two milestones are reached, consistent with the telescoping literature [21,22]. This calculation of course duration provides a rough estimate of the speed of progression through drinking milestones; a shorter course corresponds to more rapid escalation. For milestones experienced at the same age (i.e., multiple transitions occurred in the same year), course duration was coded as zero (data were not available to resolve transitions at a finer-grained level). Group differences in course duration were tested using GLMs.
