Purpose Online social networking sites (SNSs) have become a popular mode of communication between adolescents. However, little is known about the effects of social online activity on health behaviors. The authors examine the use of SNSs between friends and the degree to which SNS activities relate to face-to-face peer influences and adolescent risk behaviors. Methods Longitudinal egocentric friendship network data along with adolescent social media use and risk behaviors were collected from 1,563 tenth grade students across five Southern California high schools. Measures of online and offline peer influences were computed and assessed using fixed effects models. Results The frequency of adolescent SNS use and the number of their closest friends on the same SNS were not significantly associated with risk behaviors. However, exposure to friends’ online pictures of partying or drinking was significantly associated with both smoking (β=.07, p<.001) and alcohol use (β=.08, p<.05). While adolescents with drinking friends had higher risk levels for drinking, adolescents without drinking friends were more likely to be affected by increasing exposure to risky online pictures (β=−.10, p<.10). Myspace and Facebook had demographically distinct user characteristics and had differential effects on risk behaviors. Conclusions Exposure to risky online content had a direct impact on adolescents’ risk behaviors and significantly interacted with risk behaviors of their friends. These results provide evidence that friends’ online behaviors should be considered a viable source of peer influence and that increased efforts should focus on educating adolescents on the negative effects of risky online displays.

Friendship choices and BMI were measured for 617 adolescents (12-14 years). Overweight youth were twice as likely to have overweight friends. There was a weak association between social position and weight status, overweight youth nominated more friends but were nominated as friends less frequently than their normal weight peers.

This paper proposes several measures for bridging in networks derived from Granovetter's (1973) insight that links which reduce distances in a network are important structural bridges. Bridging is calculated by systematically deleting links and calculating the resultant changes in network cohesion (measured as the inverse average path length). The average change for each node's links provides an individual level measure of bridging. We also present a normalized version which controls for network size and a network level bridging index. Bridging properties are demonstrated on hypothetical networks, empirical networks, and a set of 100 randomly generated networks to show how the bridging measure correlates with existing network measures such as degree, personal network density, constraint, closeness centrality, betweenness centrality, and vitality. Bridging and the accompanying methodology provide a family of new network measures useful for studying network structure, network dynamics, and network effects on substantive behavioral phenomenon.

This study investigates two contagion mechanisms of peer influence based on direct communication (cohesion) versus comparison through peers who occupy similar network positions (structural equivalence) in the context of adolescents' drinking alcohol and smoking. To date, the two contagion mechanisms have been considered observationally inseparable, but this study attempts to disentangle structural equivalence from cohesion as a contagion mechanism by examining the extent to which the transmission of drinking and smoking behaviors attenuates as a function of social distance (i.e., from immediate friends to indirectly connected peers). Using the U.S. Add Health data consisting of a nationally representative sample of American adolescents (Grades 7-12), this study measured peer risk-taking up to four steps away from the adolescent (friends of friends of friends of friends) using a network exposure model. Peer influence was tested using a logistic regression model of alcohol drinking and cigarette smoking. Results indicate that influence based on structural equivalence tended to be stronger than influence based on cohesion in general, and that the magnitude of the effect decreased up to three steps away from the adolescent (friends of friends of friends). Further analysis indicated that structural equivalence acted as a mechanism of contagion for drinking and cohesion acted as one for smoking. These results indicate that the two transmission mechanisms with differing network proximities can differentially affect drinking and smoking behaviors in American adolescents.

Purpose Friendship networks are an important source of peer influence. However, existing network studies vary in terms of how they operationalize friendship and friend’s influence on adolescent substance use. This study uses social network analysis to characterize three types of friendship relations: (1) mutual or reciprocated, (2) directional, and (3) intimate friends. We then examine the relative effects of each friendship type on adolescent drinking and smoking behavior. Methods Using a saturated sample from the Add Health data, a nationally representative sample of high-school adolescents (N=2,533 nested in 12 schools), we computed the level of exposure to drinking and smoking of friends using a network exposure model, and their association with individual drinking and smoking using fixed effect models. Results Results indicated that the influence from (1) is stronger on adolescent substance use than (2), especially for smoking. Regarding the directionality of (2), adolescents are equally influenced by both nominating and nominated friends on their drinking and smoking behavior. Results for (3) indicated that the influence from “best friends” was weaker than the one from non-“best friends,” which indicates that the order of friend nomination may not matter as much as nomination reciprocation. Conclusions This study demonstrates that considering different features of friendship relationships is important in evaluating friends’ influence on adolescent substance use. Related policy implications are discussed.

Pre-exposure prophylaxis (PrEP) is efficacious to prevent HIV infection, however, uptake among young men who have sex with men (YMSM) is relatively low. The purpose of this study was to describe PrEP use and related factors in a representative sample of YMSM in two cities, Chicago and Houston. YMSM, ages 16–29, were recruited via respondent-driven sampling (RDS) from 2014–2016. Correlates of PrEP uptake were assessed in weighted multivariable logistic regression models. A total of 12.2% of participants (of 394) reported ever taking PrEP; Black YMSM had the lowest rates of uptake (4.7%) and Whites the highest (29.5%). In a multivariable regression model, having an HIV positive sex partner, reporting recent group sex, peer network size, and city (Chicago) were significantly and positively associated with use of PrEP, while Black race was negatively associated with it. Given evidence of racial/ethnic disparities in PrEP uptake in this study, further research is needed to identify potential mechanisms of action and points of intervention.

Our findings support a greater focus on friendship selection mechanisms in school-based alcohol use interventions. Social media platforms may help identify at-risk adolescent groups and foster positive norms about risk behaviors.

Purpose Consistent evidence has shown that one of the most significant influences on adolescent smoking is peer influence. There is considerable variation, however, in how peer influence is measured. This study constructs social network influence and selection variables from egocentric and sociometric data to compare their associations with smoking with considerations of perceived smoking norms and adolescent popularity. Methods Longitudinal data were collected in 9th and 10th grades in October 2006 and 2007 from predominantly Hispanic/Latino adolescents in seven southern California schools among which 1,950 adolescents completed surveys at both waves. Both cross-sectional (separately for 9th and 10th graders) and longitudinal models were estimated. Results An ego-centric measure of perceived friend smoking was strongly and consistently associated with individual smoking (AOR 1.80, p<0.001) whereas its sociometric counterpart of friend self-report smoking was only associated with smoking in 9th grade cross-sectional models (e.g., AOR=1.56, p<0.001) and rarely in longitudinal models. Popularity, measured by proportion of nominations received by class size, was associated with smoking and becoming a smoker (AOR=1.67, p<0.001) whereas perceived norms was not in longitudinal models. Friend selection was also associated with becoming a smoker (AOR=1.32, p=0.05). Conclusions This study illustrates the utility of ego-centric data for understanding peer influence and underscores the importance of perceptions and popularity as mechanisms that influence adolescent smoking.