Likelihoods for fixed rank nomination networks.

Many studies that gather social network data use survey methods that lead to censored, missing, or otherwise incomplete information. For example, the popular fixed rank nomination (FRN) scheme, often used in studies of schools and businesses, asks study participants to nominate and rank at most a small number of contacts or friends, leaving the existence of other relations uncertain. However, most statistical models are formulated in terms of completely observed binary networks. Statistical analyses of FRN data with such models ignore the censored and ranked nature of the data and could potentially result in misleading statistical inference. To investigate this possibility, we compare Bayesian parameter estimates obtained from a likelihood for complete binary networks with those obtained from likelihoods that are derived from the FRN scheme, and therefore accommodate the ranked and censored nature of the data. We show analytically and via simulation that the binary likelihood can provide misleading inference, particularly for certain model parameters that relate network ties to characteristics of individuals and pairs of individuals. We also compare these different likelihoods in a data analysis of several adolescent social networks. For some of these networks, the parameter estimates from the binary and FRN likelihoods lead to different conclusions, indicating the importance of analyzing FRN data with a method that accounts for the FRN survey design.

Stabilizing brokerage.

A variety of social and economic arrangements exist to facilitate the exchange of goods, services, and information over gaps in social structure. Each of these arrangements bears some relationship to the idea of brokerage, but this brokerage is rarely like the pure and formal economic intermediation seen in some modern markets. Indeed, for reasons illuminated by existing sociological and economic models, brokerage is a fragile relationship. In this paper, we review the causes of instability in brokerage and identify three social mechanisms that can stabilize fragile brokerage relationships: social isolation, broker capture, and organizational grafting. Each of these mechanisms rests on the emergence or existence of supporting institutions. We suggest that organizational grafting may be the most stable and effective resolution to the tensions inherent in brokerage, but it is also the most institutionally demanding.

Association between condom use at sexual debut and subsequent sexual trajectories: a longitudinal study using biomarkers.

OBJECTIVES: We compared subsequent sexual behaviors and risk of sexually transmitted infections among adolescents who did and did not use a condom at their sexual debut. METHODS: We derived data from the National Longitudinal Study of Adolescent Health, which followed a sample of 4018 sexually active adolescents between 1994 and 2002. During waves I, II, and III of the study, data on sexual behavior were gathered, and at wave III urine specimens were collected to test for sexually transmitted infections. RESULTS: Among interviewed adolescents, those who reported condom use at their debut were more likely than those who did not use condoms at their debut to report condom use at their most recent intercourse (on average 6.8 years after sexual debut), and they were only half as likely to test positive for chlamydia or gonorrhea (adjusted odds ratio=0.50; 95% confidence interval=0.26, 0.95). Reported lifetime numbers of sexual partners did not differ between the 2 groups. CONCLUSIONS: Adolescents who use condoms at their sexual debut do not report more sexual partners, are more likely to engage in subsequent protective behaviors, and experience fewer sexually transmitted infections than do adolescents who do not use condoms at their sexual debut.

Is condom use habit forming?: Condom use at sexual debut and subsequent condom use.

OBJECTIVE: The objective of this study was to assess whether using a condom at adolescent sexual debut is associated with an increased likelihood of subsequent condom use. STUDY DESIGN: A nationally representative sample was used, including 4024 sexually active adolescents (12-18 years) from the National Longitudinal Study of Adolescent Health. Logistic regression was used to model the association of condom use at sexual debut on condom use at most recent sex (mean interval, 23 months). RESULTS: Condom use at adolescent sexual debut was associated with a twofold increased likelihood of condom use during most recent sex (odds ratio, 2.28; 95% confidence interval, 1.91-2.73). CONCLUSIONS: Among adolescents, early condom use is associated with an increased likelihood of subsequent condom use.