Evaluating AIDS Prevention Programs Expanded Edition (1991) / Chapter Skim
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D Sampling and Randomization: Technical Questions about Evaluating CDC's Three Major AIDS Prevention Programs
D Sampling and Randomization: Technical Questions about Evaluating CDC's Three Major AIDS Prevention Programs
Pages 317-334
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From page 317... ...
The first section of this appendix treats the following technical issues related to sampling: the number of case studies to be used in a process evaluation of the counseling and testing program; the sample sizes needed to evaluate the effectiveness of all three programs; suggestions for controlling attntion; and the comparison of convenience samples and probability samples. The second section addresses two aspects of using randomized experiments to evaluate a project's effectiveness: successful experiments In the AIDS prevention arena and the ethics of no-treatment controls.
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From page 318... ...
In addition to addressing these sampling issues, this section includes some thoughts about using convenience samples when it is not possible to calTy out probability sampling. Number of Case Studies The purpose of conducting case studies of counseling and testing sites is to identify the variables to be considered in evaluating how well services are delivered: i.e., who is being served, do they complete the service protocol, what are the baIIiers, and so on.
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From page 319... ...
suggests the following stratification variables: · Type of facility, e.g., health department, family planning citric, drug treatment center, clinic for treatment of sexually transmitted disease, and so on (already the matrix is larger than that proposed for CBOs because of the diversity in types of setting) ; Seroprevalence rates or number of AIDS cases (i.e., low, middle, or high prevalence areas)
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From page 320... ...
Statistical texts can help investigators determine these venous factors and then use them to find the appropriate sample size, but even these specialized texts and their reference tables require an 4It should be recognized that besides merely testing the null hypothesis (that the difference between groups is zero) , one may have a particular interest in obtaining an estimate of the magnitude of the treatment effect with a given degree of precision.
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From page 321... ...
Confidentiality Guarantees Assurances of confidentiality, which should be fairly easy to guarantee in any COO study, typically have been found to decrease attrition and item nonresponse (Singer, 1978; Pane} on Privacy and Confidentiality as Factors In Survey Response, 1979~. Anonymity may be slid more successful in reducing nonresponse (Moore, Lessler, and Caspar, 1989)
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From page 322... ...
posit that survey participants must be sufficiently motivated to provide information. When the purpose of the study is perceived to be compatible with persona or social goals, compensation may not be important; however, money might motivate the respondent who feels that no other goal for participating ex~sts.5 In the AIDS prevention arena, few studies have been made on the impact of compensation to complete a study's protocol, but the studies that are available suggest that the goals or motivations of participants are indeed unportant in recruitment and attrition.
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From page 323... ...
~ fact, this method could enhance the feasibility of randomization because an investigator is likely to have a larger pool of willing study participants once members of a community learn that a given evaluation will provide them additional funds. However, the provision of the additional value would change the evaluation from a study of effectiveness to a study of efficacy.7 Cultivating and Tracking Respondents Other ways Hat have helped to avoid attrition include: familiarizing respondents at first contact with the importance and purpose of the study 6Designs that provide incentives only to participants and not to controls confound the incentive win die treatment.
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From page 324... ...
Access to respondents' social security numbers and birth dates also facilitates locating them through archival records such as voter registries, tax roils, motor vehicle records, credit bureaus, marriage licenses, real estate records, death certificates, wills, and the like. Federal agencies that remain in touch with some respondents include the Veterans Administration, the Social Secunty Admin~stration, and the Internal Revenue Service.
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From page 325... ...
A typical default assumption in a life-table analysis is that persons lost resemble persons followed from He time of loss onward, not from time 0.
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From page 326... ...
Modeling their effects, in turn, invites inferential uncertainties parallel to those that beset modeling effects in nonrandom~zed studies.) Convenience and Probability Sampling As noted In Chapter 5, We panel has recommended that CDC conduct population surveys Cat include potential and actual clients of counseling and testing services.
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From page 327... ...
did not discuss convenience samples at much length, but Me parent committee in its first report (Turner, Miller, and Moses, 1989) did review a number of nonrandom or nonprobability sample studies of gay and bisexual men and of drug users.
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From page 328... ...
Surveys have been largely limited to accidental convenience samples of subpopulations, but purposive and probability sampling have been possible. Members of drug treatment centers constitute the most accessible populations for convenience samples, and numerous examples exist of research samples drawn from methadone and detoxification clinics.
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From page 329... ...
Some researchers have purposively enlarged nonprobability samples to ensure differences among respondents. Such purposive sampling cohorts have been assembled by researchers In Portland, Oregon (Sibthorpe et al., 1989, recruited from a corrections facility, county health clinics, private welfare organizations, and street outreach)
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From page 330... ...
, who used ax-addicts to deliver AIDS health education to intravenous drug users in randomly assigned neighborhoods of Baltimore; the experimental group had significantly more knowledge at follow-up than did control group members who did not receive the intervention, although there were no significant behavioral differences. Few formal examples of randomized evaluation of street outreach studies are available in the literature; however, anecdotal reports and discussions with community-based providers indicate substantial opportunities and support for systematically testing venous strategies.
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From page 331... ...
recently reported on a successful randomized control trial In Great Bntain, In which six youth training centers were randomly assigned to receive an AIDS education comic book. No differences between the groups were detected at pretest, but at pastiest the knowledge scores of the experimental group were significantly higher.
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From page 332... ...
This strategy retains the essential parts of the service: the diagnostic technology of HIV testing and the counseling that is part of patient care.~3 At the same time, it allows for the evaluation of alternative counseling methodologies that may be found to have superior value in promoting behavioral change. In deciding whether to without a given CBO service, care must be taken to distinguish whether He service offered is an integral aspect of patient care or is an intervention of unproven worth that is available elsewhere.
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From page 333... ...
(1987) An evaluation of using ex-addict outreach workers to educate intravenous drug users about AIDS prevention.
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From page 334... ...
(1989) AIDS, Sexual Behavior, and intravenous Drug Use.
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