Presentation is loading. Please wait.

Presentation is loading. Please wait.

Recruitment and Sampling Methods in Community-Based Infectious Disease Research Crystal M. Fuller, PhD Infectious Disease Epidemiology Methods (P8462)

Similar presentations

Presentation on theme: "Recruitment and Sampling Methods in Community-Based Infectious Disease Research Crystal M. Fuller, PhD Infectious Disease Epidemiology Methods (P8462)"— Presentation transcript:

1 Recruitment and Sampling Methods in Community-Based Infectious Disease Research Crystal M. Fuller, PhD Infectious Disease Epidemiology Methods (P8462) Spring 2002

2 Lecture Overview I.Why study high-risk populations using a community- based research approach? II.Traditional sampling methods and sample selection III.Special issues in studying high-risk populations and infectious diseases (i.e., HIV, HCV, TB) IV.Sampling and recruitment methods adapted used to gain external validity in studying “hidden” or “difficult- to-reach” populations V.Conducting research among young IDUs: The REACH II Study, Baltimore, Maryland

3 High Risk Populations Infectious DiseasePopulation at risk TBHomeless Injection drug users (IDUs) HIVInjection drug users Non-injection drug users Sex workers Men who have sex w/ men (MSM; minority subgroups) Sex partners of high-risk individuals HCVInjection drug users

4 HIV Prevalence among Adult IDUs YEARAUTHOR 1987Marmor et al. 1990Caussy et al. 1990Vlahov et al. 1990Koblin et al. 1993Metzger et al. 1996Wiebel et al. 1987Chaisson et al. 1997Cheng et al. CITY (N)HIV % New York 29048% New Jersey 92635% Baltimore2,61625% Worcester 87419% Philadelphia 8818% Chicago 850 25% San Francisco 281 10% Los Angeles 3,854 2%

5 HIV Prevalence among New and Young IDUs 1988van den Hoek et al.Amsterdam15.6% (Injecting <= 5 years) 1989Friedman et al.New York22.0% (Injecting <= 5 years) 1990Vlahov et al.Baltimore15.1% (Injecting <= 18 months) 1992van Ameijden et al.Amsterdam29.2% (Injecting <= 2 years) 1996Garfein et al.Baltimore13.9% (Injecting <= 1 years)

6 HIV Incidence among Adult IDUs –199817 U.S. Cities1.5 per 100 PY (Fisher et al.) –1995Baltimore4.0 per 100 PY (Nelson et al.) –1990Chicago4.9 per 100 PY (Wiebel et al.) –1990San Francisco1.9 per 100 PY (Moss et al.)

7 HIV Incidence among Young, New IDUs Year Author Sample Characteristic Incidence ( Per 100 PY) 1992 Nicolosi et al. Italy ( 20 yrs of age) 4.9 1995 Nelson et al. Baltimore (men 34 yrs of age) 1.4 (women 34 yrs of age) 1.4 1998 Doherty et al. Baltimore ( 22 yrs of age) 2.0

8 Who’s at highest risk for HIV among IDUs? Younger age Short-term injecting career African American and Latino/a ethnicity MSM (minority subgroups) Female

9 Implementing a Research Design: Community-Based Approach Definition of Community-Based Research: Epidemiologic research which involves participant recruitment, screening, enrollment, and data collection efforts performed within a non-institutional, community setting incorporating members of the community where the research is being conducted. –Community-based clinic (STD clinic) –Community-based organization –Storefront-type setting in high-risk community

10 Traditional Sampling Methods Probability sampling –Simple random sampling –Stratified random sampling –Cluster sampling Requires that all individuals in the total population sample have a known chance of selection into the study sample

11 Application of Traditional Sampling Methods in Drug Use Research National Household Survey on Drug Abuse (NHSDA): –Multi-stage probability sample –Mail survey –Monitor prevalence and incidence of drug use;  12 yrs of age (~ 10% reporting illicit use) Monitoring for the Future (MTF): –Probability sample –School survey –Monitor prevalence and incidence of drug use among 8 th – 12 th grade students (~ 1-2% reporting illicit use)

12 Community Epidemiology Work Group (CEWG) –Community-level surveillance of drug abuse to determine nature and patterns of drug abuse and emerging trends –A network composed of researchers from major metropolitan areas of the U.S.; selected foreign countries –Death certificates, Emergency Dept, treatment admissions, urinalysis (ADAM), drug seizures, price purity, distribution, etc. (DEA) –Ethnographic research, focus groups, interviews, and other qualitative methods

13 Conducting Infectious Disease Research among High-risk Populations Populations outside existing institutional and clinic settings - “out of mainstream” or “hidden” populations Populations within institutional settings: –Treatment settings –Jails or prisons –Emergency rooms –STD clinics

14 Conducting Infectious Disease Research among High-risk Populations No known sampling frame!

15 Conducting Infectious Disease Research among High-risk Populations What happens when we use school surveys and household surveys? Major selections bias!!! –Low proportions of illicit users attending school –Low proportions of illicit users in households and may be less likely to report illicit use on a survey taken at home Homeless, transient, incarcerated, etc.

16 Conducting Infectious Disease Research among High-risk Populations What happens when we use the institutional settings known to have large numbers of drug users (i.e., treatment programs)? Major selection bias!! –Consecutive or convenience (“grab”) samples Enrollment of every individual entering a given institution in a stated study period –Approximately 15% of all IDUs are in treatment at any given time Over-sampling of a more “health-seeking” population Exclusion of non-heroin IDUs

17 Conducting Infectious Disease Research among High-risk Populations Sampling of “hidden” populations: –Street outreach methodology “Community Health Outreach Worker” (CHOW) Street-level trained staff, identify and penetrate drug user networks, identify high-risk neighborhoods, advocates and HIV educators Often ex-users, those who live within high-risk communities, and work in social services arena Late 1980’s (San Francisco) and still used today – nationally and internationally

18 Conducting Infectious Disease Research among High-risk Populations What happens when we use street outreach convenience samples? Major selection bias! –Non-treatment population –Higher risk community of drug users Potential to obtain a more diverse population –Drug type, duration of use, younger and older ages, in- and out-of-treatment, etc.

19 HIV Prevalence Rates among Treatment and Community Samples 1989 (Metzger et al.)PhiladelphiaTreatment 11.0% Community18.0% 1990-91 (Robles et al.)San JuanTreatment29.5% Community45.5% 1992(Alcabes et al.)BaltimoreTreatment27.3% Non-treatment24.3% 1992-93(Stark et al.)BerlinTreatment 3.9% Community20.7% NEP14.6%

20 Sampling Methods Adapted to the Study of “Hidden” Populations at High-risk for Blood-borne Pathogens Key-informant sampling Snowball or “chain referral” sampling Respondent-driven sampling Targeted sampling Capture-recapture sampling

21 Key-informant Sampling Key-informant Sampling: –Selecting knowledgeable respondents and asking them about behavior of others in their community and not about their own. In drug abuse research, such persons may include social workers, HIV or drug abuse counselors, public health workers, opinion leaders. Specifically designed to alleviate socially desirable responding which may arise in self-reports of sensitive information.

22 Potential Biases in Key Informant Sampling When professionals are used as key informants, their professional orientation may bias their responses. –Opinion leaders may be better options Key Informants lack detailed knowledge of their peers. Key informants may not come in contact with a representative group of peers. Only useful in exploratory studies and collection of early pilot data.

23 Snowball Sampling Snowball or “chain referral” sampling: –A study sample based on referrals made among people who share or know of others who possess some characteristics that are of research interest. (Biernacki et al., 1981) Primarily used in sociologic (qualitative) research Allows for sampling of natural interactional units

24 Snowball Sampling Identify participants (opinion leaders or key-informants) to start the chain referral; this is easily done with outreach workers or other study participants. Can accept participants who are part of a chain and those who are not. Important to keep track of index person who made the referral for later analysis on degree of clustering. May or may not want to divulge eligibility criteria to index persons.

25 Control the Types of Chains and Number of Cases in each Chain Substantive consideration: Once chains begin, an investigator may want to control the referral chains to help ensure that the general characteristics of the target population are reflected in the sample. Selective consideration: May want to exclude or limit a certain subgroup (i.e., certain age group) Theoretical consideration: What are some logical assumptions that can be made about certain groups (i.e., certain neighborhoods may use certain types of drugs and drugs purity may differ, etc.).

26 Generalizability of Snowball Sampling Can the findings be generalized to a wider population or is the sample limited? What is the extent to which snowball sampling is dependent on social networks and what types of networks?

27 Respondent Driven Sampling Respondent Driven Sampling (RDS): –A type a chain referral sampling which involves an incentive system. Reduces some of the known biases of other chain referral methods Provides a means for controlling for the biases resulting from differences in the size of personal networks

28 Respondent Driven Sampling A researcher approaches and enrolls a participant who receives an incentive for undergoing the study interview. Same participant is also given an incentive for bringing in their peers as respondents.

29 Respondent Driven Sampling Two-step process to control sampling scheme: 1) One or more members of the respondents group is promised a collective reward or threatened with a collective punishment based on whether the respondent complies. 2) Those members of the group respond to the secondary incentive by controlling the respondent – “group mediated” control. RDS produces samples that are independent of the initial participants from which the sampling begins Does not matter whether the initial sample was chosen randomly or with known biases.

30 Targeted Sampling Targeted Sampling: –A purposeful, systematic method by which controlled lists of specified populations within geographical districts are developed, and detailed plans are designed to recruit adequate numbers of cases within each of the targets. –This method uses aspects of street ethnography, theoretical sampling, stratified sampling, quota sampling, and chain referral sampling. (Watters et al., 1989) This method was designed to overcome deficiencies of chain referral models.

31 Targeted Sampling Two basic steps: 1)Field researchers (ethnographers) are deployed to map a target population; Prevents the under-representation that often results from traditional sampling approaches. 2)Field researchers (outreach workers) are deployed at diverse sites previously identified by the ethnographic mapping to recruit a known number of study participants. Further ensures that participants from different areas and subgroups will be better represented in the final sample.

32 Potential Biases in Targeted Sampling Recruiting participants during normal business hours Activities focused on more public locations (“institutional” bias may occur)

33 Targeted Sampling – Additional Approaches What do we know about drug user/using settings: –Drug scenes are neither discrete nor public –Drug activities (i.e., selling, purchasing, using) occur in concentrated areas –Mostly dispersed; occurring in private housing or vacant/abandoned buildings, or other nonpublic settings

34 Targeted Sampling – Additional Approaches Extensive ethnographic approaches: –Weight drug scenes based on their intensity of use by each category of: Drug user Time of the day Sample accordingly (could be random if numbers permit)

35 Capture-Recapture Methods Capture-Recapture: – A technique used to estimate the size of populations that are difficult to find and count, or populations that are in motion and can not be counted all at one time. (Sudman et al., 1988)

36 Capture-Recapture Methods Technique requires obtaining two or more independent observation on the same populations at the same times or based on different sources that represent the same population. The researcher needs to know three things: –# of persons observed at the first time –# of persons observed at the second time –Total # of persons observed at both times Those captured must be “tagged” in some way so that it may be determined if they were included both captures.

37 Capture-Recapture Methods Assumptions: –Equal probability of being sampled during the study period Different individuals can be missed in the counting process for various reasons. –Independence between counts: observing an individual at one time has no effect on the event of observing the individual at a second. Being missed once can often be correlated with being missed a second time. –Population size does not change in composition or size during the study period (“closed population model”). Population being studied changes between captures; “open population model”; need at least four captures.

38 What Happens in Real Life???? Depends… –How “hidden” is the population? –How much do you know as a researcher about the target population? –Are there collaborations that can be developed to find out more about the target populations?

39 Who’s at highest risk for HIV among IDUs? Younger and/or recently initiated IDUs!

40 Young, Recently Initiated IDUs Baltimore, Maryland, 1997-1999 REACH II Study Collaborative Injection Drug User Study (CIDUS II) Multisite Cohort Study –Baltimore, MD –Chicago, IL –Los Angeles, CA –New Orleans, LA –New York, NY (Harlem) –New York, NY (Lower East Side)

41 Recruitment Methodology Eligibility: –15-30 years of age –Injected at least once in past 6 months –Injected ≤ 5 years Cohort study design –Baseline, 6-month, 12-month follow-up visits

42 Sampling and Recruitment Methodology Convenience sample –Modified target sampling –Community street outreach –Modified respondent driven / chain referral Enrolled each participant through a 2-stage screening process

43 Sampling and Recruitment Methodology Modified target sampling: –Community Advisory Board Social Services, Health Care Workers, CBO representatives, HIV and drug counselors, etc. –Seasoned outreach staff –Opinion leaders identified by outreach staff

44 Sampling and Recruitment Methodology Modified target sampling: –Identified 12 high-risk neighborhoods in Baltimore City known to be frequented by young IDUs –Conducted “mobile” recruitment over a 2-year period 1997-1999 using a study van

45 Sampling and Recruitment Methodology Parked the REACH II Van in 4 different sites per week and revisited those same 4 sites each week –Once a site “dried up”, we went to the next site –Ensured that each site was utilized during summer months –Extended hours in certain sites based on visibility of young users Goal: Enroll every young IDU in Baltimore City!

46 Sampling and Recruitment Methodology Community street outreach: –Outreach staff went out and recruited potential participants within a 3-block radius of the mobile site –Posted and distributed flyers on abandoned buildings, ER, homeless shelters, NEP, STD Clinics, treatment centers, etc. –Conducted “stage one” of screening process

47 Sampling and Recruitment Methodology Modified respondent driven / chain referral: –Identified participants who had additional access to other young IDUs and gave incentives to the participant for bringing in young users. Shooting gallery managers Other young IDUs (< 25 years of age)

48 Sampling and Recruitment Methodology Keep track of how each participant entered the study! Selection bias can be assessed and considered when interpreting study findings.

49 Study Findings Screened 276 young IDUs 82% were eligible and enrolled (n=226) 61% female! 64% Black 11% HIV seropositive 65% HCV seropositive

50 REACH II Study Findings HIV seroincidence:6.6 per 100 PY HCV seroincidence:22.3 per 100 PY Extremely high-risk population!

Download ppt "Recruitment and Sampling Methods in Community-Based Infectious Disease Research Crystal M. Fuller, PhD Infectious Disease Epidemiology Methods (P8462)"

Similar presentations

Ads by Google