Background-There is a large and persistent racial disparity in STI in the U.S. which has placed n... more Background-There is a large and persistent racial disparity in STI in the U.S. which has placed non-Hispanic-Blacks at disproportionately high risk. We tested a hypothesis that both individuallevel risk factors (partner number, anal sex, condom use) and local-network features (concurrency and assortative mixing by race) combine to account for the association between race and chlamydia status. Methods-Data from the Longitudinal Survey of Adolescent Health Wave III were used. Chlamydia status was determined using biomarkers. Individual-level risk behaviors were selfreported. Network location variables for concurrency and assortative mixing were imputed using egocentrically sample data on sexual partnerships. Results-After controlling for demographic attributes including age, sex, marital status, education and health care access there remained a strong association between race and chlamydia status (OR = 5.23, 95% CI] 3.83-7.15], p < .001 for Non-Hispanic Blacks with Non-Hispanic Whites as the reference category). The inclusion of individual-level risk factors did not alter the association between race and chlamydia(OR = 5.23 for Non-Hispanic Blacks). The inclusion of concurrency and assortative mixing by race substantially reduced the association between race and chlamydia status (OR = 1.87, 95% CI [0.89-3.91] p > .05 for Non-Hispanic Blacks).
Journal of Acquired Immune Deficiency Syndromes, Aug 1, 2021
Background:Volatility in sexual contact rates has been recognized as an important factor influenc... more Background:Volatility in sexual contact rates has been recognized as an important factor influencing HIV transmission dynamics. One-time partnerships may be particularly important given the potential to quickly accumulate large number of contacts. Yet, empirical data documenting individual variation in contact rates remains rare. This study provides much needed data on temporal variation in one-time partners to better understand behavioral dynamics and improve the accuracy of transmission models.Methods:Data for this study from a longitudinal cohort study of young men who have sex with men (MSM) and transgender women in Chicago. Participants provided sexual network data every 6-months for 2 years. A series of random effects models examined variation in one-time partnership rates and disaggregated within and between associations of exposure variables. Exposure variables included prior number of one-time partners, number of casual partners, and having a main partner.Results:Results indicated substantial between and within person variation in one-time partners. Casual partnerships were positively associated and main partnerships negatively association with one-time partnership rates. There remained a small positive association between prior one-time partnerships and the current number of one-time partnerships.Conclusions:Despite the preponderance of a low number of one-time partners, substantial variation in one-time partnership rates exists among young MSM and transgender women. Accordingly, focusing on high contact rate individuals alone may be insufficient to identify periods of highest risk. Future studies should utilize these estimates to more accurately model how volatility impacts HIV transmission and better understand how this variation influences intervention effectiveness.
medRxiv (Cold Spring Harbor Laboratory), Nov 29, 2020
Seroadaptive behaviors help to reduce HIV risk for some men who have sex with men (MSM), and have... more Seroadaptive behaviors help to reduce HIV risk for some men who have sex with men (MSM), and have been well documented in a range of MSM populations. Advancements in biomedical prevention have changed the contexts in which seroadaptive behaviors occur. We thus sought to estimate and compare the prevalence of four stages of the "seroadaptive cascade" in the recent era: knowledge of own serostatus, knowledge of partner serostatus; serosorting (matching by status), and condomless anal intercourse. Serosorting overall appeared to remain common, especially with casual and one-time partners. Although PrEP use did not impact status discussion, it did impact serosorting and the likelihood of having condomless anal intercourse. For respondents not diagnosed with HIV and not on PrEP, condomless anal intercourse occurred in just over half of relationships with partners who were not on treatment. Biomedical prevention has intertwined with rather than supplanted seroadaptive behaviors, while contexts involving neither persist.
To recruit participants, we placed banner and text-based pop-up advertisements in English and Spa... more To recruit participants, we placed banner and text-based pop-up advertisements in English and Spanish on social media, male-male geosocial networking, and general LGBTQ-interest apps and websites. Advertisements on all platforms were targeted based on location in Washington, and advertisements on social media were additionally targeted to males who reported an interest in relationships with men or expressed an interest in LGBTQ-related topics or groups.
In this paper, we present an overview and descriptive results from one of the first egocentric ne... more In this paper, we present an overview and descriptive results from one of the first egocentric network studies of men who have sex with men (MSM) from across the United States: the ARTnet study. ARTnet was designed to support prevention research for human immunodeficiency virus (HIV) and other sexually transmitted infections (STIs) that are transmitted across partnership networks. ARTnet implemented a population-based egocentric network study design that sampled egos from the target population and asked them to report on the number, attributes, and timing of their sexual partnerships. Such data provide the foundation needed for parameterizing stochastic network models that are used for disease projection and intervention planning. ARTnet collected data online from 2017 to 2019, with a final sample of 4904 participants who reported on 16198 sexual partnerships. The aims of this paper were to characterize the joint distribution of three network parameters needed for modeling: degree distributions, assortative mixing, and partnership age, with heterogeneity by partnership type (main, casual and one-time), demography, and geography. Participants had an average of 1.19 currently active partnerships ("mean degree"), which was higher for casual partnerships (0.74) than main partnerships (0.45). The mean rate of one-time partnership acquisition was 0.16 per week (8.5 partners per year). Main partnerships lasted 272.5 weeks on average, while casual partnerships lasted 133.0 weeks. There was strong but heterogenous assortative mixing by race/ethnicity for all groups. The mean absolute age difference for all partnership types was 9.5 years, with main partners differing by 6.3 years compared to 10.8 years for casual partners. Our analysis suggests that MSM may be at sustained risk for HIV/STI acquisition and transmission through high network degree of sexual partnerships. The ARTnet network study provides a robust and reproducible foundation for understanding the dynamics of HIV/STI epidemiology among U.S. MSM and supporting the implementation science that seeks to address persistent challenges in HIV/STI prevention.
Substantial changes in human immunodeficiency virus (HIV)-related sexual behavior have been repor... more Substantial changes in human immunodeficiency virus (HIV)-related sexual behavior have been reported by virtually every survey of homosexual/bisexual men in the last decade. This paper uses a behavior-based simulation to examine how such changes are likely to affect the long-term future of the acquired immunodeficiency syndrome (AIDS) epidemic among homosexual men. Data from the Longitudinal AIDS Impact Project in New York City are used to estimate age-specific patterns of unprotected anogenital contact and behavioral change from 1980 to 1991. Model projections are validated using New York City surveillance data on AIDS incidence from 1981 to 1991. The current levels of unsafe sex reported in the Longitudinal AIDS Impact Project are shown to be almost exactly on the epidemic threshold. If this behavior were maintained, HIV prevalence would slowly decline in the population, but with just one additional unsafe sexual partner per year HIV would instead become endemic, with seroprevalence of about 65% in the oldest group and about 25% in the youngest. Transmission dynamics in the youngest group are analyzed in detail. For this group, the assortative age-matching bias in partner selection patterns raises the unsafe behavior threshold slightly in the long run.
Because AIDS is a sexually-transmitted disease (STD), most prevalent in the prime childbearing ye... more Because AIDS is a sexually-transmitted disease (STD), most prevalent in the prime childbearing years, and because the epidemic has become generalized throughout Sub-Saharan Africa, it is generally recognized that many orphans will be generated by the AIDS epidemic.
medRxiv (Cold Spring Harbor Laboratory), Feb 13, 2022
doi: medRxiv preprint NOTE: This preprint reports new research that has not been certified by pee... more doi: medRxiv preprint NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice.
Temporal exponential-family random graph models (TERGMs) are a flexible class of network models f... more Temporal exponential-family random graph models (TERGMs) are a flexible class of network models for the dynamics of tie formation and dissolution. In practice, separable TERGMs (STERGMs) are the subclass most often used, as these permit estimation from inexpensive cross-sectional study designs, and benefit from approximations designed to reduce the computational burden (Carnegie et al., 2015). Improving the approximations are the focus of this paper. We extend the work of Carnegie et al. (2015), which addressed the problem of constructing a STERGM with two specific equilibrium properties: a cross-sectional distribution defined by a given exponential-family random graph model (ERGM), and tie durations defined by given constant hazards of dissolution. We start with Carnegie et al.'s observation that the exact result is tractable in the dyad-independent case, and then show that taking the sparse limit of the exact result leads to a different approximation than the one they presented. We show that the new approximation outperforms theirs for sparse, dyadindependent models, and that for dyad-dependent models the errors tend to increase
ABSTRACTBackgroundMean active degree is an important proxy measure of cross-sectional network con... more ABSTRACTBackgroundMean active degree is an important proxy measure of cross-sectional network connectivity commonly used in HIV/STI epidemiology research. No current studies have compared measurement methods of mean degree using cross-sectional surveys for men who have sex with men (MSM) in the United States.MethodsWe compared mean degree estimates based on reported ongoing main and casual sexual partnerships (current method) against dates of first and last sex (retrospective method) from 0–12 months prior to survey date in ARTnet, a cross-sectional survey of MSM in the U.S. (2017–2019). ARTnet collected data on the number of sexual partners in the past year but limited reporting on details used for calculating mean degree to the 5 most recent partners. We used linear regression to understand the impact of truncated partnership data on mean degree estimation.ResultsRetrospective method mean degree systematically decreased as the month at which it was calculated increased from 0–12 m...
Background: The speed with which a pathogen circulates in a sexual network is a function of netwo... more Background: The speed with which a pathogen circulates in a sexual network is a function of network connectivity. Cross-sectional connectivity is a function of network features like momentary degree and assortative mixing. Temporal connectivity is driven by partner acquisition rates. The forward-reachable path (FRP) has been proposed as a summary measure of these two aspects of transmission potential. We use empirical data from San Francisco and Atlanta to estimate the generative parameters of the FRP and compare results to the HIV/sexually transmitted infection epidemics in each city. Methods: We used temporal exponential random graph models to estimate the generative parameters for each city’s dynamic sexual network from survey data. We then simulated stochastic dynamic networks from the fitted models and calculated the FRP for each realization, overall, and stratified by partnership type and demographics. Results: The overall mean and median paths were higher in San Francisco tha...
ABSTRACTBackgroundThe potential speed through which a pathogen may circulate in a network is a fu... more ABSTRACTBackgroundThe potential speed through which a pathogen may circulate in a network is a function of network connectivity. Network features like degree (number of ongoing partnerships) determine the cross-sectional network connectivity. The overall transmission potential of a pathogen involves connectivity over time, which can be measured using the forward reachable path (FRP). We modeled dynamic sexual networks of MSM in San Francisco and Atlanta to estimate the FRP as a predictor of HIV/STI epidemic potential.MethodsWe used exponential random graph models to obtain parameter estimates for each city’s sexual network and then simulated the complete networks over time. The FRP was estimated in each city overall and stratified by demographics.ResultsThe overall mean and median FRPs were higher in San Francisco than in Atlanta, suggesting a greater epidemic potential for HIV and STIs in San Francisco. At one year, in both cities, the average FRP among casual partnerships was high...
Work with longitudinal network survey data and the dynamic network outputs of the statnet ERGMs h... more Work with longitudinal network survey data and the dynamic network outputs of the statnet ERGMs has demonstrated the need for consistent frameworks and data structures for expressing, storing, and manipulating information about networks that change in time. Motivated by our requirements for exchanging data among researchers and various analysis and visualization processes, we have created an R package dynamicnetwork that builds upon previous work in the network, statnet and sna packages and provides a limited functional implementation. This paper discusses design issues and considerations, describes classes and forms of dynamic data, and works through several examples to demonstrate the utility of the package. The functionality of the rSoNIA package that uses dynamicnetwork to exchange data with the Social Network Image Animator (SoNIA) software to create animated movies of changing networks from within R is also demonstrated.
AIDS education and prevention : official publication of the International Society for AIDS Education, 1995
This article examines how networks of social and sexual relations affect risky sexual behavior an... more This article examines how networks of social and sexual relations affect risky sexual behavior and HIV seroprevalence among young gay men. Social networks can transmit information and cultural norms regarding safer sex, while networks of sexual partners channel the risk of exposure to HIV infection. These two network effects may help to explain some of the behavior and seroconversion differentials in the gay community. A number of recent studies have shown higher rates of unsafe sex among younger gay men. In the Longitudinal AIDS Impact Project, for example, younger gay men (18-24) report unsafe receptive anal sex at rates double that for any other age group (30% vs. 14-16%). One possible explanation is that younger men have watched fewer friends and colleagues contract HIV or AIDS, and are correspondingly less cautious. We test this hypothesis by comparing the personal networks of younger and older gay men to see whether those who practice safer sex have more exposure to persons wi...
This chapter describes the comparative local network data collected in two related studies of HIV... more This chapter describes the comparative local network data collected in two related studies of HIV-related behaviors in Uganda and Thailand in the mid-1990s. The Thai survey was based on a cluster sample of about 1,700 17–45 year old low-income men, and about 700 female commercial-sex workers. The Ugandan survey used a representative household-based cluster sample of about 1,600 men and women aged 15–49 from the district of Rakai. The local network module was very similar in the two surveys, collecting information on the attributes of the respondents and their three most recent sexual partners, attributes of the partnerships, geographic network information, and behaviors within the partnerships. The chapter reviews the study design, fieldwork experience and measurement of network characteristics, and concludes by presenting a sampling of findings from studies using the network data.
The ergm package supports the statistical analysis and simulation of network data. It anchors the... more The ergm package supports the statistical analysis and simulation of network data. It anchors the statnet suite of packages for network analysis in R introduced in a special issue in Journal of Statistical Software in 2008. This article provides an overview of the new functionality in the 2021 release of ergm version 4. These include more flexible handling of nodal covariates, term operators that extend and simplify model specification, new models for networks with valued edges, improved handling of constraints on the sample space of networks, and estimation with missing edge data. We also identify the new packages in the statnet suite that extend ergm's functionality to other network data types and structural features and the robust set of online resources that support the statnet development process and applications.
This chapter describes the network data collected by the CEP-CPC Study of Social Change in Nang R... more This chapter describes the network data collected by the CEP-CPC Study of Social Change in Nang Rong, Thailand in 1994-95. The purpose of the study was to monitor and understand the sweeping demographic and social changes occurring in this province. The data collection included a community profile, household survey, and migrant follow-up in 51 villages with over 7,300 households and 42,000 persons. The household survey collected kin and agricultural support network data within and between villages, with household geographic coordinates; all households within a village were surveyed, so the within-village networks are complete. The chapter reviews the study design, fieldwork experience and measurement of network characteristics, and concludes by presenting a sampling of findings from studies using the network data.
The strength of the evidence linking concurrency to HIV epidemic severity in southern and eastern... more The strength of the evidence linking concurrency to HIV epidemic severity in southern and eastern Africa led the Joint United Nations Programme on HIV/AIDS and the Southern African Development Community in 2006 to conclude that high rates of concurrent sexual partnerships, combined with low rates of male circumcision and infrequent condom use, are major drivers of the AIDS epidemic in southern Africa. In a recent article in the Journal of the International AIDS Society, Larry Sawers and Eileen Stillwaggon attempt to challenge the evidence for the importance of concurrency and call for an end to research on the topic. However, their "systematic review of the evidence" is not an accurate summary of the research on concurrent partnerships and HIV, and it contains factual errors concerning the measurement and mathematical modelling of concurrency. Practical prevention-oriented research on concurrency is only just beginning. Most interventions to raise awareness about the risks of concurrency are less than two years old; few evaluations and no randomized-controlled trials of these programmes have been conducted. Determining whether these interventions can help people better assess their own risks and take steps to reduce them remains an important task for research. This kind of research is indeed the only way to obtain conclusive evidence on the role of concurrency, the programmes needed for effective prevention, the willingness of people to change behaviour, and the obstacles to change.
Background-There is a large and persistent racial disparity in STI in the U.S. which has placed n... more Background-There is a large and persistent racial disparity in STI in the U.S. which has placed non-Hispanic-Blacks at disproportionately high risk. We tested a hypothesis that both individuallevel risk factors (partner number, anal sex, condom use) and local-network features (concurrency and assortative mixing by race) combine to account for the association between race and chlamydia status. Methods-Data from the Longitudinal Survey of Adolescent Health Wave III were used. Chlamydia status was determined using biomarkers. Individual-level risk behaviors were selfreported. Network location variables for concurrency and assortative mixing were imputed using egocentrically sample data on sexual partnerships. Results-After controlling for demographic attributes including age, sex, marital status, education and health care access there remained a strong association between race and chlamydia status (OR = 5.23, 95% CI] 3.83-7.15], p < .001 for Non-Hispanic Blacks with Non-Hispanic Whites as the reference category). The inclusion of individual-level risk factors did not alter the association between race and chlamydia(OR = 5.23 for Non-Hispanic Blacks). The inclusion of concurrency and assortative mixing by race substantially reduced the association between race and chlamydia status (OR = 1.87, 95% CI [0.89-3.91] p > .05 for Non-Hispanic Blacks).
Journal of Acquired Immune Deficiency Syndromes, Aug 1, 2021
Background:Volatility in sexual contact rates has been recognized as an important factor influenc... more Background:Volatility in sexual contact rates has been recognized as an important factor influencing HIV transmission dynamics. One-time partnerships may be particularly important given the potential to quickly accumulate large number of contacts. Yet, empirical data documenting individual variation in contact rates remains rare. This study provides much needed data on temporal variation in one-time partners to better understand behavioral dynamics and improve the accuracy of transmission models.Methods:Data for this study from a longitudinal cohort study of young men who have sex with men (MSM) and transgender women in Chicago. Participants provided sexual network data every 6-months for 2 years. A series of random effects models examined variation in one-time partnership rates and disaggregated within and between associations of exposure variables. Exposure variables included prior number of one-time partners, number of casual partners, and having a main partner.Results:Results indicated substantial between and within person variation in one-time partners. Casual partnerships were positively associated and main partnerships negatively association with one-time partnership rates. There remained a small positive association between prior one-time partnerships and the current number of one-time partnerships.Conclusions:Despite the preponderance of a low number of one-time partners, substantial variation in one-time partnership rates exists among young MSM and transgender women. Accordingly, focusing on high contact rate individuals alone may be insufficient to identify periods of highest risk. Future studies should utilize these estimates to more accurately model how volatility impacts HIV transmission and better understand how this variation influences intervention effectiveness.
medRxiv (Cold Spring Harbor Laboratory), Nov 29, 2020
Seroadaptive behaviors help to reduce HIV risk for some men who have sex with men (MSM), and have... more Seroadaptive behaviors help to reduce HIV risk for some men who have sex with men (MSM), and have been well documented in a range of MSM populations. Advancements in biomedical prevention have changed the contexts in which seroadaptive behaviors occur. We thus sought to estimate and compare the prevalence of four stages of the "seroadaptive cascade" in the recent era: knowledge of own serostatus, knowledge of partner serostatus; serosorting (matching by status), and condomless anal intercourse. Serosorting overall appeared to remain common, especially with casual and one-time partners. Although PrEP use did not impact status discussion, it did impact serosorting and the likelihood of having condomless anal intercourse. For respondents not diagnosed with HIV and not on PrEP, condomless anal intercourse occurred in just over half of relationships with partners who were not on treatment. Biomedical prevention has intertwined with rather than supplanted seroadaptive behaviors, while contexts involving neither persist.
To recruit participants, we placed banner and text-based pop-up advertisements in English and Spa... more To recruit participants, we placed banner and text-based pop-up advertisements in English and Spanish on social media, male-male geosocial networking, and general LGBTQ-interest apps and websites. Advertisements on all platforms were targeted based on location in Washington, and advertisements on social media were additionally targeted to males who reported an interest in relationships with men or expressed an interest in LGBTQ-related topics or groups.
In this paper, we present an overview and descriptive results from one of the first egocentric ne... more In this paper, we present an overview and descriptive results from one of the first egocentric network studies of men who have sex with men (MSM) from across the United States: the ARTnet study. ARTnet was designed to support prevention research for human immunodeficiency virus (HIV) and other sexually transmitted infections (STIs) that are transmitted across partnership networks. ARTnet implemented a population-based egocentric network study design that sampled egos from the target population and asked them to report on the number, attributes, and timing of their sexual partnerships. Such data provide the foundation needed for parameterizing stochastic network models that are used for disease projection and intervention planning. ARTnet collected data online from 2017 to 2019, with a final sample of 4904 participants who reported on 16198 sexual partnerships. The aims of this paper were to characterize the joint distribution of three network parameters needed for modeling: degree distributions, assortative mixing, and partnership age, with heterogeneity by partnership type (main, casual and one-time), demography, and geography. Participants had an average of 1.19 currently active partnerships ("mean degree"), which was higher for casual partnerships (0.74) than main partnerships (0.45). The mean rate of one-time partnership acquisition was 0.16 per week (8.5 partners per year). Main partnerships lasted 272.5 weeks on average, while casual partnerships lasted 133.0 weeks. There was strong but heterogenous assortative mixing by race/ethnicity for all groups. The mean absolute age difference for all partnership types was 9.5 years, with main partners differing by 6.3 years compared to 10.8 years for casual partners. Our analysis suggests that MSM may be at sustained risk for HIV/STI acquisition and transmission through high network degree of sexual partnerships. The ARTnet network study provides a robust and reproducible foundation for understanding the dynamics of HIV/STI epidemiology among U.S. MSM and supporting the implementation science that seeks to address persistent challenges in HIV/STI prevention.
Substantial changes in human immunodeficiency virus (HIV)-related sexual behavior have been repor... more Substantial changes in human immunodeficiency virus (HIV)-related sexual behavior have been reported by virtually every survey of homosexual/bisexual men in the last decade. This paper uses a behavior-based simulation to examine how such changes are likely to affect the long-term future of the acquired immunodeficiency syndrome (AIDS) epidemic among homosexual men. Data from the Longitudinal AIDS Impact Project in New York City are used to estimate age-specific patterns of unprotected anogenital contact and behavioral change from 1980 to 1991. Model projections are validated using New York City surveillance data on AIDS incidence from 1981 to 1991. The current levels of unsafe sex reported in the Longitudinal AIDS Impact Project are shown to be almost exactly on the epidemic threshold. If this behavior were maintained, HIV prevalence would slowly decline in the population, but with just one additional unsafe sexual partner per year HIV would instead become endemic, with seroprevalence of about 65% in the oldest group and about 25% in the youngest. Transmission dynamics in the youngest group are analyzed in detail. For this group, the assortative age-matching bias in partner selection patterns raises the unsafe behavior threshold slightly in the long run.
Because AIDS is a sexually-transmitted disease (STD), most prevalent in the prime childbearing ye... more Because AIDS is a sexually-transmitted disease (STD), most prevalent in the prime childbearing years, and because the epidemic has become generalized throughout Sub-Saharan Africa, it is generally recognized that many orphans will be generated by the AIDS epidemic.
medRxiv (Cold Spring Harbor Laboratory), Feb 13, 2022
doi: medRxiv preprint NOTE: This preprint reports new research that has not been certified by pee... more doi: medRxiv preprint NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice.
Temporal exponential-family random graph models (TERGMs) are a flexible class of network models f... more Temporal exponential-family random graph models (TERGMs) are a flexible class of network models for the dynamics of tie formation and dissolution. In practice, separable TERGMs (STERGMs) are the subclass most often used, as these permit estimation from inexpensive cross-sectional study designs, and benefit from approximations designed to reduce the computational burden (Carnegie et al., 2015). Improving the approximations are the focus of this paper. We extend the work of Carnegie et al. (2015), which addressed the problem of constructing a STERGM with two specific equilibrium properties: a cross-sectional distribution defined by a given exponential-family random graph model (ERGM), and tie durations defined by given constant hazards of dissolution. We start with Carnegie et al.'s observation that the exact result is tractable in the dyad-independent case, and then show that taking the sparse limit of the exact result leads to a different approximation than the one they presented. We show that the new approximation outperforms theirs for sparse, dyadindependent models, and that for dyad-dependent models the errors tend to increase
ABSTRACTBackgroundMean active degree is an important proxy measure of cross-sectional network con... more ABSTRACTBackgroundMean active degree is an important proxy measure of cross-sectional network connectivity commonly used in HIV/STI epidemiology research. No current studies have compared measurement methods of mean degree using cross-sectional surveys for men who have sex with men (MSM) in the United States.MethodsWe compared mean degree estimates based on reported ongoing main and casual sexual partnerships (current method) against dates of first and last sex (retrospective method) from 0–12 months prior to survey date in ARTnet, a cross-sectional survey of MSM in the U.S. (2017–2019). ARTnet collected data on the number of sexual partners in the past year but limited reporting on details used for calculating mean degree to the 5 most recent partners. We used linear regression to understand the impact of truncated partnership data on mean degree estimation.ResultsRetrospective method mean degree systematically decreased as the month at which it was calculated increased from 0–12 m...
Background: The speed with which a pathogen circulates in a sexual network is a function of netwo... more Background: The speed with which a pathogen circulates in a sexual network is a function of network connectivity. Cross-sectional connectivity is a function of network features like momentary degree and assortative mixing. Temporal connectivity is driven by partner acquisition rates. The forward-reachable path (FRP) has been proposed as a summary measure of these two aspects of transmission potential. We use empirical data from San Francisco and Atlanta to estimate the generative parameters of the FRP and compare results to the HIV/sexually transmitted infection epidemics in each city. Methods: We used temporal exponential random graph models to estimate the generative parameters for each city’s dynamic sexual network from survey data. We then simulated stochastic dynamic networks from the fitted models and calculated the FRP for each realization, overall, and stratified by partnership type and demographics. Results: The overall mean and median paths were higher in San Francisco tha...
ABSTRACTBackgroundThe potential speed through which a pathogen may circulate in a network is a fu... more ABSTRACTBackgroundThe potential speed through which a pathogen may circulate in a network is a function of network connectivity. Network features like degree (number of ongoing partnerships) determine the cross-sectional network connectivity. The overall transmission potential of a pathogen involves connectivity over time, which can be measured using the forward reachable path (FRP). We modeled dynamic sexual networks of MSM in San Francisco and Atlanta to estimate the FRP as a predictor of HIV/STI epidemic potential.MethodsWe used exponential random graph models to obtain parameter estimates for each city’s sexual network and then simulated the complete networks over time. The FRP was estimated in each city overall and stratified by demographics.ResultsThe overall mean and median FRPs were higher in San Francisco than in Atlanta, suggesting a greater epidemic potential for HIV and STIs in San Francisco. At one year, in both cities, the average FRP among casual partnerships was high...
Work with longitudinal network survey data and the dynamic network outputs of the statnet ERGMs h... more Work with longitudinal network survey data and the dynamic network outputs of the statnet ERGMs has demonstrated the need for consistent frameworks and data structures for expressing, storing, and manipulating information about networks that change in time. Motivated by our requirements for exchanging data among researchers and various analysis and visualization processes, we have created an R package dynamicnetwork that builds upon previous work in the network, statnet and sna packages and provides a limited functional implementation. This paper discusses design issues and considerations, describes classes and forms of dynamic data, and works through several examples to demonstrate the utility of the package. The functionality of the rSoNIA package that uses dynamicnetwork to exchange data with the Social Network Image Animator (SoNIA) software to create animated movies of changing networks from within R is also demonstrated.
AIDS education and prevention : official publication of the International Society for AIDS Education, 1995
This article examines how networks of social and sexual relations affect risky sexual behavior an... more This article examines how networks of social and sexual relations affect risky sexual behavior and HIV seroprevalence among young gay men. Social networks can transmit information and cultural norms regarding safer sex, while networks of sexual partners channel the risk of exposure to HIV infection. These two network effects may help to explain some of the behavior and seroconversion differentials in the gay community. A number of recent studies have shown higher rates of unsafe sex among younger gay men. In the Longitudinal AIDS Impact Project, for example, younger gay men (18-24) report unsafe receptive anal sex at rates double that for any other age group (30% vs. 14-16%). One possible explanation is that younger men have watched fewer friends and colleagues contract HIV or AIDS, and are correspondingly less cautious. We test this hypothesis by comparing the personal networks of younger and older gay men to see whether those who practice safer sex have more exposure to persons wi...
This chapter describes the comparative local network data collected in two related studies of HIV... more This chapter describes the comparative local network data collected in two related studies of HIV-related behaviors in Uganda and Thailand in the mid-1990s. The Thai survey was based on a cluster sample of about 1,700 17–45 year old low-income men, and about 700 female commercial-sex workers. The Ugandan survey used a representative household-based cluster sample of about 1,600 men and women aged 15–49 from the district of Rakai. The local network module was very similar in the two surveys, collecting information on the attributes of the respondents and their three most recent sexual partners, attributes of the partnerships, geographic network information, and behaviors within the partnerships. The chapter reviews the study design, fieldwork experience and measurement of network characteristics, and concludes by presenting a sampling of findings from studies using the network data.
The ergm package supports the statistical analysis and simulation of network data. It anchors the... more The ergm package supports the statistical analysis and simulation of network data. It anchors the statnet suite of packages for network analysis in R introduced in a special issue in Journal of Statistical Software in 2008. This article provides an overview of the new functionality in the 2021 release of ergm version 4. These include more flexible handling of nodal covariates, term operators that extend and simplify model specification, new models for networks with valued edges, improved handling of constraints on the sample space of networks, and estimation with missing edge data. We also identify the new packages in the statnet suite that extend ergm's functionality to other network data types and structural features and the robust set of online resources that support the statnet development process and applications.
This chapter describes the network data collected by the CEP-CPC Study of Social Change in Nang R... more This chapter describes the network data collected by the CEP-CPC Study of Social Change in Nang Rong, Thailand in 1994-95. The purpose of the study was to monitor and understand the sweeping demographic and social changes occurring in this province. The data collection included a community profile, household survey, and migrant follow-up in 51 villages with over 7,300 households and 42,000 persons. The household survey collected kin and agricultural support network data within and between villages, with household geographic coordinates; all households within a village were surveyed, so the within-village networks are complete. The chapter reviews the study design, fieldwork experience and measurement of network characteristics, and concludes by presenting a sampling of findings from studies using the network data.
The strength of the evidence linking concurrency to HIV epidemic severity in southern and eastern... more The strength of the evidence linking concurrency to HIV epidemic severity in southern and eastern Africa led the Joint United Nations Programme on HIV/AIDS and the Southern African Development Community in 2006 to conclude that high rates of concurrent sexual partnerships, combined with low rates of male circumcision and infrequent condom use, are major drivers of the AIDS epidemic in southern Africa. In a recent article in the Journal of the International AIDS Society, Larry Sawers and Eileen Stillwaggon attempt to challenge the evidence for the importance of concurrency and call for an end to research on the topic. However, their "systematic review of the evidence" is not an accurate summary of the research on concurrent partnerships and HIV, and it contains factual errors concerning the measurement and mathematical modelling of concurrency. Practical prevention-oriented research on concurrency is only just beginning. Most interventions to raise awareness about the risks of concurrency are less than two years old; few evaluations and no randomized-controlled trials of these programmes have been conducted. Determining whether these interventions can help people better assess their own risks and take steps to reduce them remains an important task for research. This kind of research is indeed the only way to obtain conclusive evidence on the role of concurrency, the programmes needed for effective prevention, the willingness of people to change behaviour, and the obstacles to change.
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Papers by Martina Morris