title: Identification of trajectories of social network composition change and the relationship to alcohol consumption and norms.
abstract: BACKGROUND
  College drinking is embedded in a social context, drawing attention to the effects of social network composition on consumption. The presence of heavy drinking friends in social networks predicts later alcohol misuse, but little is known about how the composition of one's social network composition changes over time. This study identified changes in social network composition in a sample of at-risk students and examined the relationship among network trajectories, alcohol consumption, and descriptive norms.
  
  
  METHODS
  Participants were 503 students (64% male) mandated to participate in an alcohol prevention intervention for residence hall alcohol policy violations. At baseline, students provided self-report data about alcohol consumption, perceived peer drinking norms, and peer alcohol involvement. Parallel assessments were completed at 6- and 12-months post-baseline.
  
  
  RESULTS
  Growth-mixture models identified four groups of individuals with similar levels of heavy drinkers in their social networks. The majority of students had stable or decreasing numbers of heavy drinkers in their networks across the study, whereas two groups reported relatively stable densities of heavy drinkers from baseline to 6-months and increasing densities from 6- to 12-months. At baseline, the four groups were generally equivalent on consumption and normative perceptions. At 6- and 12-months, however, the groups differed significantly on consumption and norms.
  
  
  CONCLUSIONS
  These results suggest that changes in the number of heavy drinkers in college students' social networks may have significant implications for at-risk drinking.
authors.affiliation: Yale University School of Medicine, Department of Psychiatry, New Haven, CT 06511, United States. kelly.demartini@yale.edu
authors.forename: Kelly S
authors.initials: KS
authors.lastname: DeMartini
authors.forename: Mark A
authors.initials: MA
authors.lastname: Prince
authors.forename: Kate B
authors.initials: KB
authors.lastname: Carey
mesh_terms: D000428:Alcohol Drinking / Q000523:psychology*; D000437:Alcoholism / Q000523:psychology; D003627:Data Interpretation, Statistical; D005006:Ethnicity; D005260:Female; D033062:Friends; D006801:Humans; D008297:Male; D010379:Peer Group; D012016:Reference Values; D012931:Social Environment; D012959:Socioeconomic Factors; D013334:Students; D014495:Universities; D055815:Young Adult
keywords: Alcohol prevention; College drinking; Descriptive norms; Social networks; Trajectories