This work differed from other studies of adolescent friendship networks and substance use in several potentially important ways. First, four assessments per year is unusual, though not unprecedented (e.g., Knecht et al., 2011, also obtained four assessments, but only for a single year). Our data showed some tendency to select fewer alters over time, which may have reflected survey fatigue, because participants would learn that every alter selected as someone you spend free time with would be followed up with further questions. The absolute average participation decline of about 25% from wave 1 to wave 8 is not trivial, and its absolute significance is unclear. It is somewhat reassuring that parameter estimates for the three schools for which fewer than eight waves of data were available were not different from the other schools.
