Estimating Sexual Behavior Parameters from Routine Sexual Behavior Data
Van Vliet, Carina, Van der Ploeg, Catharina P. B., Kidula, Nancy, Malonza, Isaac M., Tyndall, mark, Nagelkerke, Nico J. D., The Journal of Sex Research
The advent of the HIV/AIDS epidemic has greatly stimulated the study of sexual behavior. Empirical behavior studies such as surveys (e.g., ACSF investigators, 1992; Catania, Coates & Turner, 1992; Cleland & Ferry, 1995; Moses, Muia & Bradley, 1994) have gained popularity and have been recognised by the World Health Organization as an important health related activity (World Health Organization; 1989). Mathematical models relating sexual behavior and disease parameters, such as the duration of infectivity, to the epidemiology of HIV and other sexually transmitted diseases (STDs) have also gained interest beyond academia (Rothenberg, 1997). Such models are useful tools in understanding more precisely the epidemiology of these infections, in predicting their impact and the success of interventions, and thereby assisting the design of more effective public health policy. Mathematical models have also indicated the need for an improved understanding of sexual behavior and the role of sexual networks and mixing patterns (Gupta, Anderson, & May, 1989; Kault, 1993; Morris, 1995; Morris, Podhista, Wawer, & Handcock, 1996; Yorke & Hetchcote, 1978).
In many mathematical models for the spread of STDs (Ghani, Swinton, & Garnett, 1996; Morris & Kretzschmar, 1995; Watts & May, 1992) parameters of interest with respect to sexual behavior include the rate of acquisition of new partners', and concurrency that is, the number of simultaneous sexual partnerships an individual has at a given time. In routine surveys of sexual behavior, however, questions on these variables are not always asked. Instead, individuals are often requested to report the total number of sex partners they have had over a specific period T (e.g. the previous year, or the previous 3 months). Under serial monogamy, the number of new sex partners an individual has during T equals either the total number of sex partners during T minus 1 if the individual was in a partnership at the beginning of the period T, or the total number of sex partners during T if the individual was not in a partnership at the beginning of this period.
However, in many societies serial monogamy is neither norm nor practice. Evidence for high levels of concurrency in some African populations has emerged from recent sexual behavior studies in Uganda, where about 40% of the total population reports at least one concurrent partnership when the last three sexual partners were examined (Morris, Sewankambo, Wawer, Serwadda & Lainjbo, 1995). In Western societies, where serial monogamy might be the norm for large sections of the population, partnerships may overlap: For instance, a survey in The Netherlands showed that 6.4% of men had sex outside of a steady partnership in the previous year (Van Zessen & Sandfort, 1991). Concurrency in partnerships has been shown to have a considerable impact on the spread of HIV and other STDs (Garnett & Johnson, 1997; Moms & Kretzschmar, 1995, 1997; Watts & May, 1992).
For concurrent partnerships, the sexual behavior parameters relevant to mathematical modelling usually cannot be derived directly from traditional surveys of sexual behavior or from data now routinely collected in clinical settings. Awareness of the importance of the rate of partner acquisition and concurrency for understanding sexual behavior has led to improved surveys of sexual behavior. For example, the British National Survey of Sexual Attitudes and Lifestyle uses innovative instruments for data collection that allow the direct estimation of all relevant parameters: Detailed information about the timing of the last three sex partners is solicited from respondents (Johnson, Wadsworth, Wellings, & Field, 1993). Surveys using a similar or more extensive local sexual-network design have been performed in the United States (Laumann, Gagnon, Michael, & Michaels, 1994), Uganda (Wawer, 1993), and Thailand (Wawer, 1990). …