Examining the social and behavioral dynamics of substance use in a longitudinal network study in rural Appalachia.

BACKGROUND: Prior studies have shown that individuals and their peers often have similar substance use behaviors, but the mechanisms driving these similarities - particularly in rural settings, are not well understood. The primary objectives of this analysis are to (1) identify factors that contribute to relationship turnover and maintenance within a rural network of persons who use drugs (PWUD), (2) determine whether assimilation and/or homophily shape participants use of injection drugs, heroin, and stimulants (methamphetamine and cocaine), and (3) assess the extent that these mechanisms influence networks ties and/or behaviors and whether these effects vary across time. METHODS: Sociometric network data were collected from a cohort of PWUD in rural Eastern Kentucky at baseline (2008-2010) and at four follow-up visits conducted approximately semiannually. Stochastic actor-oriented models (SAOMS) were used to model network structure and participant behaviors as jointly dependent variables and to identify characteristics associated with the maintenance, dissolution, and formation of network ties and changes in drug use behaviors. RESULTS: Findings suggest (1) greater network stability over time for reciprocal and transitive relationships, (2) both homophily and assimilation played a greater role in shaping injection drug use (IDU) initiation and cessation than they did in shaping heroin and stimulant use, and (3) the importance of these mechanisms appeared consistent over time. CONCLUSION: Given the stability of particular network structures and evidence of both homophily and assimilation with respect to drug-use behaviors, interventions that leverage social networks could be used to motivate health-promoting behaviors.

Extent and implications of omitted ties on network measures in a longitudinal social network survey of people who use drugs.

BACKGROUND: Previous research has revealed under-reporting of personal network members (i.e., alters) in studies involving people who use drugs (PWUD). This analysis (1) characterizes relationships that were more likely to be omitted but later recalled with prompting and (2) identifies network structural characteristics most impacted by these omissions among a sample of PWUD in rural Appalachian Kentucky, an epicenter of the opioid epidemic. METHODS: Data were collected through longitudinal assessments as part of the Social Networks Among Appalachian People (SNAP) study (2008-2017). Study participants completed interviewer-administered questionnaires that collected social network data via free-listing at baseline and six-month intervals. At visit 5, after free-listing, interviewers prompted participants with the names of previously reported alters. We used modified Poisson regression with generalized estimating equations to identify individual- and relationship-level characteristics associated with an alter being reported only after prompting. We examined the impact of including vs. excluding relationships reported after prompting on local and global sociometric network measures (i.e., betweenness centrality, bridging, density, mean degree, transitivity, cliques, and 2-cores). RESULTS: Relationships reported only after prompting were more likely to be immediate family (Adjusted Prevalence Ratio [APR]:1.29; 95% Confidence Interval [CI]: 1.03-1.63) and less likely to involve sex (APR:0.54; 95% CI: 0.43-0.67). Considerable differences were observed for participant positional rankings of betweenness centrality and bridging, and differences in network density and average degree pre- and post-prompting were statistically significant. CONCLUSION: Longitudinal network studies that aim to assess transmission dynamics, information diffusion, or peer influence should consider the effects of omitted relationships.

Wild Bornean orangutan (Pongo pygmaeus wurmbii) feeding rates and the Marginal Value Theorem.

The Marginal Value Theorem (MVT) is an integral supplement to Optimal Foraging Theory (OFT) as it seeks to explain an animal's decision of when to leave a patch when food is still available. MVT predicts that a forager capable of depleting a patch, in a habitat where food is patchily distributed, will leave the patch when the intake rate within it decreases to the average intake rate for the habitat. MVT relies on the critical assumption that the feeding rate in the patch will decrease over time. We tested this assumption using feeding data from a population of wild Bornean orangutans (Pongo pygmaeus wurmbii) from Gunung Palung National Park. We hypothesized that the feeding rate within orangutan food patches would decrease over time. Data included feeding bouts from continuous focal follows between 2014 and 2016. We recorded the average feeding rate over each tertile of the bout, as well as the first, midpoint, and last feeding rates collected. We did not find evidence of a decrease between first and last feeding rates (Linear Mixed Effects Model, n = 63), between a mid-point and last rate (Linear Mixed Effects Model, n = 63), between the tertiles (Linear Mixed Effects Model, n = 63), nor a decrease in feeding rate overall (Linear Mixed Effects Model, n = 146). These findings, thus, do not support the MVT assumption of decreased patch feeding rates over time in this large generalist frugivore.