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The Research Teams: Project Descriptions
A brief description of the invited research teams and their projects is attached. Each of the teams has been actively engaged in the collection and analysis of network data over a long time (often a decade or more) or across multiple national contexts. The projects span the range from random sample local network designs to partial network tracing samples, to saturation samples for complete networks. The primary focus is on the role of networks in HIV and STD transmission, but some projects focus on mobility and others on general health-related behavior. COMPLETE NETWORK DESIGNS The Nang Rong Projects
The Nang Rong Projects are a loosely integrated collection of studies designed to monitor and understand the sweeping demographic, social, and environmental changes that have taken place over the past twenty years in Nang Rong, Thailand. The foci are fertility and contraceptive behavior, life course choices, migration processes, and land use. An interest in social networks in relation to these demographic and social processes informs much of the work. Social network data in the Nang Rong Projects come mainly from surveys administered in 1994 and 1995. There were three such surveys: a household survey (n= 42,219 current and former members of 7,337 households in 51 villages); a migrant follow-up (n= 1,781 out-migrants from 22 villages); and a community profile (n= 310 villages). Another round of surveys is scheduled for 2000 and 2001, which will expand the scope and temporal depth of the social network data and enable an examination of network change over time. The 1994/95 Nang Rong surveys provide information about multiple social relations, at multiple levels of observation. The village data include information on ties between villages based on sharing temples, schools, water sources, bus routes, and access to major highways as well as those arising directly from labor exchanges and equipment rental. The household data include information on ties to other households based on sibling relationships, help with the last rice harvest; the renting, hiring, and sharing of agricultural equipment, and prior residence as well as those arising indirectly from the use of local rice mills and membership in village organizations. The migrant data include information on contact with other migrants from the origin villages, visits and exchanges of money and goods with origin households, sibling ties, and some ego-based questions about friends and acquaintances in the place of destination. A distinctive feature of the Nang Rong data is the availability of data on complete population-based social networks. Many important measures of network structure and position, such as subgroups and their membership, indirect connections between network members via paths containing intermediaries, and some kinds of network positions can only be calculated from complete networks. Information about social ties was collected for all households in the study villages, and for all villages in Nang Rong District. Household and village identifiers are explicitly recorded. For households, the availability of complete data provides replicated social networks for 51 villages. A great strength of the data is the rich information on characteristics of households (e.g., size and composition, contraceptive choices of married women, agricultural activities) and villages (e.g., resources, social institutions, health care) that can be used to help interpret network patterns at both household and village level and to understand variation in network patterns across villages. Data from the 1994/95 survey have also been incorporated into a
Geographic Information System (GIS). Geographic information
about village locations makes it possible to properly orient the
graphs of the village networks and study variability in their spatial
arrangement. Insights into patterns of network ties can be
gained by mapping village networks in reference to landcover data
derived from remote images. The spatial analytic capabilities
of the GIS also make it possible to assess the impact of the
administratively defined district boundary and to evaluate whether
rivers and perennial streams create barriers to network ties between
villages.
The National Longitudinal Study of Adolescent Health (Add Health)
Add Health is a survey designed to assess the health status of adolescents in the United States and explore the effects of the multiple contexts or environments (both social and physical) in which they live. The primary sampling frame was a national list of high schools. A sample of 80 eligible high schools was selected. The survey consisted of two parts: an "in-school" questionnaire, completed by all of the students in the sampled schools (more than 90,000 adolescents), and an "in-home" questionnaire, completed by a sample of students in each school (about 12,000 adolescents). For 16 "saturation" schools, all enrolled students were selected for both the in-school and in-home interviews (about 6,000 adolescents). The in-school questionnaire asked students to nominate up to five
male and five female friends, to locate and record their student
numbers, and to indicate which of five activities they had done with
each of these friends during the past week. For students in the
saturated schools, a more extensive friendship and romantic
relationship history was elicited in the in-home questionnaire.
Because the nominations can be matched to student rosters, this
yields nearly complete social network data for most schools.
Friendship networks can be determined and a respondent's peer group,
as well as his or her position within it, can be described in
detail.
PARTIAL NETWORK DESIGNS
Social networks of heterosexuals at high risk of HIV: The
Colorado Springs Study
This project, begun in the fall of 1987, was the first prospective
study of the influence of social network structure on the propagation
of infectious disease. Funded by the Centers for Disease
Control to explore the dynamics of HIV transmission in heterosexual
populations, its intellectual father was Klovdahl, who formally
proposed application of the social network paradigm to infectious
disease epidemiology. The primary sampling frame consisted of
heterosexuals perceived to be at high risk for HIV: prostitute
women, injecting drug users, and their respective sexual and
illicit-drug partners. Participants were recruited from health
department STD, HIV, and substance abuse clinics; vice squad
referrals; street outreach; and frequently named partners of
participants (cross-links). Enrollment was continuous from 1988
through 1991 with participants being scheduled for annual repeat
blood testing and interviews (up to 5 years). Participants were
asked to nominate (full names and locating information)
socio-familial, sexual, and drug partners for the 6-month period
preceding interview, to complete a face-to-face questionnaire, and to
provide a blood sample for HIV, syphilis, and hepatitis
testing. Of 1079 eligible persons, 595 (55%) participants were
enrolled. In 990 interviews, they named nearly 7,000 persons as
contacts or associates (in a community of 400,000 population).
About two-thirds of the contacts could be uniquely identified, and
half of the remaining cases are known not to be duplicates
duplicates. This large data set permits cross-sectional and
dynamic analyses of the structure of social and risk networks, while
blood test results permit analysis of factors facilitating or
constraining disease transmission.
The Atlanta and Flagstaff Network Studies
This is a group of four related studies. The first in focused on the interrelationship of drug-related and sex-related risk for HIV in Atlanta and Flagstaff. We used a standardized (though not necessarily uniform) approach to the ascertainment of networks of persons who use drugs and have sex together in a rural (Flagstaff AZ) and urban (Atlanta GA) setting. Many of the data collection methods were based on the Colorado Springs study. Some of the field methods were altered, to be less oriented toward the contact tracing process, and more toward defining the larger social/sexual/drug-using sociogram in which respondents were embedded. To facilitate this "next generation" approach, we focused on three communities that were definable, bounded, and accessible. In each we established two community "chains" of persons, using a combination snowball and chain-link sampling method. We interviewed and initial person (the "seed") and sought all of his/her contacts for interview as well. One of these persons was chosen as the next link (either randomly, in half the chains, or by nomination in the other half). The third link was then chosen from one of the contacts to the second, and so forth to obtain a toal of ten links. All the contacts to persons in positions 1, 4, 7 , and 10 were interviewed. In the course of the study, we also interviewed a number of "isolates," persons who were not formally named by anyone but who, ethnographically, appeared to be related to the group. We enrolled a total of 292 persons, of whom 226 were members of community chains that we followed over a 3-year period. We obtained at least two interviews on 76% of the 226 respondents in the community chains. We have conducted a supplemental study, using a snowball design, that compares what persons say about the interactions among their partners with what their partners say about themselves (the matrix interview). The design of this study consisted of a straightforward, two-wave snowball constructed from five initial "seeds, with a total of 275 persons named in the study. The initial results suggest that only about 12% of the relationships identified by respondents among their partners are verified by the partners themselves, but that the structure identified by the matrix interview is similar to that which emerges from the more comprehensive snowball evaluation. A third study in Atlanta uses network ascertainment as a portion of its evaluation. In a series of 240 persons with AIDS treated at the city's primary AIDS clinic, we are conducting a study of the factors that affect adherence to antiretroviral regimens. Sampling is straightforward: a clinic sample, stratified by gender and major risk category, is used, and information on demographics, medical background, psychological stataus, comorbidity, clinical course, pharmacological regimens and adherence to these regimens is obtained. In addition, we request information on the individual's personson network of friends, sexual, and drug-using partners. A fourth study, just begun, will evaluate personal and network
factors in the acquisition of STDs among adolescents recruited using
street ethnographic methods. The basic design here is a dynamic
cohort: 60 persons at ages 15, 16, 17, and 18 will be initially
recruited and followed for three years. Each year, an
additional 60 15-year olds will be added to the group. Since
these young people will be recruited from a definably geographic
neighborhood, we expect considerable "recursion" in their sexual and
drug using connections, and hope to demonstrate the role of network
dynamics and structure in the transmission of multiple STDs.
The Seattle "Sexual Mixing", "Sexual Networks", and "Sexual Partnership
Types" Studies
This group of studies are designed to describe the sexual mixing patterns, the sexual networks, and the specific types of sexual partnerships among Seattle populations with and without sexually transmitted diseases. The populations covered include attendees at STD clinics; attendees at non-STD health facilities; partners of STD infected individuals reached through contact tracing; respondents recruited at socio-geographically specified areas of the city; as well as representative samples of the general population based on census tract of residence. The data make it possible to examine mixing patterns by race, age
and geographic areas, and to analyze the impact of mixing on the risk
of infection. We can also examine whether the impact of mixing
differs by type of infection (e.g., bacterial vs. viral, or genital
warts vs. genital herpes), or reverse the question and compare
network composition across groups defined by infection status.
As partner information is collected both from the original
respondent, and from the enrolled partners, we are in a position to
compare the two reports. Finally, we can use the qualitative
data to examine the motives that lead adolescents and adults into
specific types of partnerships and networks. In addition to
empirical analyses, we have used our data in a number of modelling
exercises in collaboration with Geoff Garnett. In many ways all of
the above investigations are currently ongoing.
LOCAL NETWORK DESIGNS
The National Health and Social Life Survey and Chicago Health
and Social Life Survey
Both the National Health and Social Life Survey (NHSLS) and the Chicago Health and Social Life Survey (CHSLS) collected extensive information on sexual networks as well as the practices that occurred within these relations. The CHSLS was conducted from 1995 through 1997 and was conceived as a complement to the NHSLS, which was conducted in 1992. Both projects employed face-to-face interviews and targeted women and men between 18 and 59 years of age. The NHSLS was a national multistage area probability sample designed to give each U.S. household a known probability of inclusion. The CHSLS was also representative, but drew samples at two geographic levels: the city level, which includes an inner suburban ring, and four targeted-neighborhood areas within the City of Chicago. The response rate was 78.6% for the NHSLS and ranged from 60% to 78% for the Chicago samples. In addition to interviewer-administered questions, both surveys included self-administered sections to improve response rates on potentially sensitive topics such as same-gender sexual experiences and drug use. The total number of cases was 3,432 in the NHSLS and 2,114 in the CHSLS. Regarding networks, the CHSLS features recent, localized sexual and social friendship networks, while the NHSLS is a national sample with more extensive information about lifetime sexual networks. For each respondent the NHSLS included information on sexual
behavior such as the number of sexual partners, the frequency of sex,
varieties and patterns of sexual practices (e.g., oral, anal, and
vaginal sexual practices), basic demographic information on up to 28
lifetime sexual partners, and detailed demographic and sexual
information on up to two last-year partners. This rich, diverse set
of information about respondents' partners makes sexual network
analysis feasible. The NHSLS also gathered self-reported data
on health-related characteristics, including nine common sexually
transmitted diseases (STDs), sexual dysfunction, and sexual
victimization. The CHSLS asked many of the same basic questions
as the NHSLS, but also included new sections on social networks (up
to six confidants of respondents), geographic location, institutional
actors, and relationship characteristics for the respondent's two
most recent sexual partners. The social network information in the
CHSLS is likely to be particularly useful for building intervention
and prevention programs since information about STDs is transmitted
through both social and sexual networks. The Ugandan and Thai Local Sexual Network Studies
These two surveys employ local network methodology. They have different sampling populations, but both have a comparable questionnaire module for collecting local sexual network information. The Thai survey was conducted in 1992-3. Three populations were sampled by quota: low income men in three communities (n=1,075 15-49 years old, urban, intermediate and rural); long-haul truckers in two sites (n=330, 15 yo and up); and women working in inexpensive brothels in two sites (n=678, 12-53 yo). The Ugandan survey was community based, using 90 communities in the Rakai district of southern Uganda, stratified into rural, intermediate and trading center (n=1628, men and women 15-45 yo). Dwellings were enumerated and chosen at random, and a Kish table was used to select the respondent within the household. Both surveys used the same name generator -- the person you had sex with most recently (and previous to this) -- collecting information on up to three most recent sexual partners. The Ugandan survey also collected information on the first sexual partner. Information included attributes of the alter, attributes of the relationship, and the partner-specific behavioral repertoire. The structure of the modules is roughly comparable to the NHSLS above. The Ugandan module contained 77 questions per partner, the Thai somewhat less. The local network design makes it possible to examine questions of
assortative mixing by age, geographic residence, and other
attributes. These data can be used to drive simulations to
understand the role of network segmentation in population
transmission dynamics. The information on relationship interval
makes it possible to examine the pattern of concurrent
partnerships. These data, too, can be used to drive simulations
to examine the links between concurrency and component size, and the
impacts on disease spread . The pair-specific behavior
reveals both within- and between- person differences in risk
taking. The comparability in the two surveys makes it possible
to do substantial comparative work in each of these areas,
highlighting the variations in the social organization of sexuality,
and their impact on the population dynamics of HIV and other
STIs.
The WHO/UNAIDS 4 Cities Study
This is a comparative population based study in four African towns with markedly different levels of HIV infection. The study sites were selected on the basis of the HIV prevalence among pregnant women and trends over time of this prevalence. As high HIV prevalence towns Kisumu (Kenya) and Ndola (Zambia) were selected. The low HIV prevalence towns are Cotonou (Benin) and Yaoundé (Cameroon). Examination of the trends of HIV prevalence over time suggests that the current differences in prevalence are due to differences in rate of spread of the virus rather than differences in time since the start of the epidemic. By 1985 11% of pregnant women in Kampala (Uganda) and 2% of pregnant women in Ndola were HIV infected. Nine years later, in 1994, the prevalence of HIV infection in pregnant women in Kisumu, Kampala and Ndola was over 25%, whereas in Cotonou and in Yaoundé it was still far below 5% (0.6% and 2.7% respectively). The surveys took place between July 1997 and March 1998. In each of the towns households were selected by two stage cluster sampling. All men and women aged 15 to 40 years, who slept in the house the night before the visit by the study team, were included in the study. The target for sample size in each site was 1,000 men and 1,000. Households were visited by a team consisting of interviewers and nurses
or doctors. Study participants were interviewed on their socio-demographic
characteristics and sexual behaviour, using a standardized questionnaire.
The questions on sexual behaviour included questions on characteristics
of the spouse and of any extramarital partners in the past 12 months. Following
information was collected on the extramarital partnerships: type of relationship
in the respondent's own words; age, education and ethnic group of the partner;
duration of partnership and number of sex acts; exchange of money for sex;
condom use; whether the partner had other partners. Men were also interviewed
about past and present symptoms of sexually transmitted diseases (STD's)
and health seeking behaviour. After the interview study participants
were requested to give a blood sample, which was tested for HIV, syphilis
and HSV-2; and a urine sample, which was tested for gonorrhoea and chlamydial
infection.
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