NIMH/APPC Workgroup On Behavioral and Biological Outcomes in HIV/STD Prevention Studies

Abstract

SELF-REPORTED BEHAVIORS have often been the primary outcome measures in behavioral-prevention studies designed to reduce the further transmission of HIV and AIDS. Because it is often assumed that study participants may not always provide truthful or accurate responses to sensitive questions about their sexual or drug-use behaviors, it has been argued that behavioral self-reports are insufficient for the evaluation of the success of an intervention. Thus, the claim has been made that results of these studies can only be accepted if there is a biologic outcome measure that can serve to corroborate self-reported behavior change. Moreover, it is asserted that biologic outcome data provide a meaningful public health outcome, and must be assessed before prevention programs can be widely adopted. Although most would agree that HIV seroincidence would be the strongest evidence used to assess the public health impact of HIV-prevention studies, this assessment is often not possible if there is a low incidence of HIV in the population being studied. Thus, many have recommended that sexually transmitted diseases (STDs) should be used as surrogate markers for HIV, despite the fact that the true empirical relationship between a given STD and HIV has not been established. Indeed, the relationship between the incidence and prevalence of a given STD and HIV incidence is no less complex than the relationship between self-reported behavior and HIV incidence. Increasing correct and consistent condom use or decreasing the prevalence of an STD could, under the right circumstances, decrease the transmissibility of HIV. The magnitude of such a decrease will depend on several factors, including the prevalence of HIV and the sexual mixing patterns (i.e., partner selection) in the population. Given the complexity of these relationships, mathematical models of HIV transmission have been developed to help clarify the role of behavior change and STD-control programs in the prevention of HIV transmission. The National Institute of Mental Health and the Annenberg Public Policy Center convened the Workgroup on Behavioral and Biologic Outcomes in HIV/STD Prevention Studies to consider some of these issues and to provide guidance to the research community. The workgroup was charged to address questions about the validity of self-reported behaviors, the sensitivity and specificity of STD diagnostic tests, and the relationship among behavioral measures, STDs, and HIV. The workgroup was also asked to consider the utility of HIV transmission models, and the possible similarities and differences among these models. Finally, members of the workgroup were asked to outline some future directions for research that would sharpen the understanding of these issues. These questions are addressed systematically in this position statement. How Valid Are Self-Report Data on Condom Use, Number of Partners, and Other Behavioral Measures of HIV Risk, and How Can We Maximize the Validity of These Measures? In using self-reports of behavior, two psychometric aspects of the measurement instrument are of greatest concern: (1) reliability (is the instrument free of random error?); and (2) validity (is the instrument measuring what we think it is measuring; i.e., is the instrument free of both random and systematic error?). Self-reports of the frequency of sex, condom use, and the number of sexual partners typically involve characterizations by an individual of behavior during a given period. A self-report can be incorrect either because the person does not accurately recall his or her behavior during that period, or because the person fails to truthfully report behavior that is accurately recalled. In general, people will provide truthful responses if they are (1) assured that their responses will be anonymous or held confidential, such that their names will ultimately not be associated with their responses; (2) provided with a set of motivating instructions that stress the importance of honest responding, underscore the importance of honest responding for the scientific integrity of the research project, and emphasize the scientific importance of the project in general; (3) not asked to report their behavior in a face-to-face context, but rather indicate their responses in a way that others will not directly observe their answers in the immediate situation; and (4) asked to sign a pledge of truthfulness before undertaking the interview or questionnaire. Given these conditions, most persons will provide what they believe are truthful responses, although some levels of untruthfulness may still occur in certain populations for certain socially taboo or stigmatized behaviors. The workgroup recommended that the above practices be adopted where possible, and that a valid measure of social desirability response tendency be routinely included in behavioral assessments to provide an indication of potential failures to be truthful, and which can be included as a covariate in statistical analyses, where appropriate. Given truthful responding, the accuracy of recall will be affected by a number of factors, including the length of the period for which recall is requested, the question format, and individual difference variables (e.g., reports might be less accurate for persons who engage in behaviors with a high degree of frequency). It is commonly assumed that persons will have more accurate recall for shorter durations; however, recent research suggests that this may not always be the case, and that moderate durations (3-6 months) may be preferable to shorter (1 month) or longer (1 year) durations. Another common assumption is that persons provide frequency judgments by thinking about individual episodes of the behavior during the time frame in question, and then mentally tally the behavior to report an overall frequency. Although some persons may do so, others invoke rule-based heuristics to generate frequencies (e.g., “I typically engage in sex twice a week, so the number of times I have engaged in sex in the past three months is 2 × 12 = 24”). Certain question formats encourage episodic versus rule-based thinking, and the use of different cognitive strategies in making frequency judgments can affect recall accuracy. Accuracy of recall may also be affected by the person's educational level or age, the appropriateness of the methods of assessment for the question being asked (e.g., variability of individual behavior is best captured by a diary), demand characteristics of the situation, and by the use of alcohol or drugs either chronically or contemporaneously with the sexual activity. Although each of these variables can impact the accuracy of recall, the weight of the scientific evidence to date suggests that properly administered self-reports of sexual frequency, condom-use frequency, condom-use consistency, and the number of sexual partners during a moderate time frame can yield reasonably accurate indices of these behaviors, which can be used for a wide range of scientific studies. However, research suggests that a small percentage of persons may still provide highly inaccurate responses. Residual analyses and other statistical procedures can be used to help identify these persons. It is important to note that self-reports of behavior can be useful outcome measures even if they are subject to some inaccuracy. Accuracy of self-reports can be characterized at either the aggregate (group) level or the individual level. At the aggregate level, the concern is whether the mean or median number of reported sexual-risk activities for a group of individuals corresponds to the true mean or median of sexual risk activities for that group. At the individual level, the interest is whether the self-report of sexual-risk activities for a given person corresponds to the actual sexual-risk activities of that person. A self-report measure can be inaccurate at the individual level, yet still provide useful data at the aggregate level (e.g., if some individuals overestimate their frequency of sex and others underestimate this frequency, it is possible for the overestimations to cancel the underestimations, thereby yielding an accurate representation of the mean or median). Inaccuracy in self-reports may not pose a problem for scientific questions in which a degree of inaccuracy can be tolerated. For example, if the interest is to compare mean shifts in condom use for persons randomly assigned to an experimental or control group, and if all self-reports tend to underestimate actual behavior by 10% to 15%, this bias will be present in both groups, and it will not affect the estimate of the mean difference in true condom use between groups. In this case, problems of partial inaccuracy would be problematic if the nature of the bias differs in the experimental and control groups. A common focus of research is to identify social and psychological correlates of behavioral tendencies to engage in unprotected sex. In this case, the self-report measures need to reasonably map onto the true score and be sufficiently free of measurement error, so that correlations with other constructs are not meaningfully biased. It is possible to use self-reports to accurately measure behavior change; however, there are many reasons why biologic data may not be congruent with self-reports. Thus, failure to find a simple linear relationship between condom use and incident STDs cannot be taken as an indication of “lying” or “inaccuracy” on the part of the respondent; indeed, epidemiologic models of transmission would suggest a true nonlinear relationship. In addition, although respondents may truthfully (and accurately) report 100% condom use, they may have been using condoms incorrectly (e.g., not put on at initiation of sex, put on the wrong way and then flipped over, taken off after ejaculation but sexual activity continued), or the condom may have slipped off, leaked, or broken. Incorrect condom use with high-risk partners could result in incident STDs. Clearly, attempts to link behavior to STD incidence cannot rely solely on a categorical “yes” or “no” response. Behavioral scientists need to develop methods to assess correct as well as consistent condom use. Despite this shortcoming, there was consensus among the members of the workgroup that when appropriate assessment conditions are established, well-designed questions concerning sexual-risk behaviors result in reasonably reliable and valid self-reports. How Good Is the Sensitivity and Specificity of Laboratory Tests of HIV and STDs, and What is Their Predictive Value When Used in Field Trials? Sensitivity refers to the ability of a diagnostic test to identify the true positives, or persons that are actually infected, whereas specificity refers to the ability of the test to identify the true negatives, or persons that are not infected. The organisms most commonly used to evaluate the effectiveness of a behavior-change intervention are the curable bacterial infections Neisseria gonorrhoeae and Chlamydia trachomatis. These organisms offer two advantages: they are highly prevalent in many settings, and have sufficiently high incidence to make outcome measurements more practical. Because the infections are easily curable with a single-dose oral antibiotic regimen, determination of incidence is facilitated by a strategy of screening, treatment, and re-screening at desired intervals. The following STDs have also been used in cumulative incidence or prevalence studies and to verify virginity in younger populations: Trichomonas vaginalis. This organism is common in some populations. On a practical level, infection detection is limited to women, and asymptomatic infection is common. Culture and modification of some polymerase chain reaction (PCR) tests by adding primers to other commercially available tests have been used to enhance diagnosis. Bacterial vaginosis. This is an ecological alteration of the vaginal flora and not a true sexually transmitted infection. Because of high prevalence and high incidence of posttreatment recurrence, this STD may be a better marker of sexual activity than of incident infection. Syphilis. Syphilis serology may be useful in some study groups, but as with the viral serologies, it requires repeated collection of a blood specimen with confirmatory testing. In most areas-even in those with high STD morbidity-the incidence of syphilis is too low to be useful as an outcome measure in behavioral intervention studies. Chronic viral infections can also be used as outcome measures, but require the identification of incident infections. Human immunodeficiency virus and many other viral STDs (e.g., herpes simplex virus, human papillomavirus) result in lifelong infection, which makes the differentiation of incidence and prevalence difficult. Incidence is typically assessed by to identify which makes assessment more and simplex virus 2 This infection can be a outcome measure because of high prevalence and incidence in populations and groups. The occur in transmission is by transmission blood use. Incidence is decreasing as more widely of this is more to practices than to sexual transmission. Human The incidence of is high in and detection may be a marker for sexual activity in this group. However, serology further and evaluation before it can be used as an outcome in a more accurate of and the for and specimen collection have methods collection of by highly can be using methods such as (1 to 2 2 after or vaginal These methods of asymptomatic populations in settings, and make of research The of tests on are highly although other may offer The sensitivity of a test is to for and to for the The HIV tests used in (i.e., and and in research (PCR) also have sensitivity and Because there are commercially available tests and to enhance the ability of other to study the use of tests is are more easily made the results of a available tests and an The test is for both and and the is for The for and the for are Despite all some and results will suggest that the specificity of these tests the of ability to measure The by 100% sensitivity are to but must be taken in study For example, if sensitivity of the test is to and sensitivity of the test is to after of to of the prevalence will be In addition, the to failures for infections that were and need to be infections after the intervention would be as incident (e.g., must control for to The specificity and sensitivity results reported are on tests in results in studies, it is to control in the and of the to the Behavioral that biologic the research require STD during all of the study and the use of a must be under certain conditions and must be the study is in an an appropriate must be or reliable procedures to the of the at the time the diagnostic tests are the of a study with HIV/STD involve the prevalence and incidence of STDs or HIV in the population. prevalence or incidence is a may be which will to testing. are on of before that can be used to reduce the of diagnosis. was consensus among the members of the workgroup that the specificity and sensitivity of all HIV diagnostic tests and of most STD diagnostic tests are Although studies pose a in specimen the are not if and are Given reliable and valid self-reports of behavior and sensitive and diagnostic tests for STDs, the question of the between these measures must be What Are the HIV and Other The of an HIV-prevention intervention is to reduce HIV incidence. HIV infection is facilitated by the of other STDs. A consistent of empirical data has that (e.g., and diseases (e.g., the risk of incident HIV infection by to However, the results of intervention studies HIV infection STD control are which suggests that the biologic and epidemiologic relationship is The impact of STD control on HIV incidence may be affected by the prevalence of STDs or HIV and by the behavioral characteristics of the population (e.g., patterns of condom a population STDs an important role in HIV incidence in where transmission in a population with high STD incidence. transmitted diseases a role in the of HIV infection among Although STDs a role in HIV transmission among they may an important role in the transmission of HIV to sexual partners of Thus, although a in STD incidence or prevalence can reduce HIV a simple relationship between STD and HIV does not under most Although this fact questions the utility of using STD data as a surrogate for HIV it does not the utility of using STD data to that sexual transmission of a has been by an intervention. What Are the Condom and STDs When used and condoms can reduce the incidence of STDs, including HIV. data to this are studies of that indicate a in among consistent condom However, as reports of consistent condom use do not always correct use. Because there are for in condom use, study should questions that assess the and aspects of condom use. as the relationship between STD and HIV is so too is the relationship between behavior and STDs The transmission of a sexually transmitted infection is on individual number of sexual number of transmissibility of the infection, and the infection of the For example, unprotected sex with an partner will not result in the transmission of an infection. further there is evidence that people tend to engage in behaviors with partners they as and in behavior with partners they as For example, persons often use condoms with and partners but not with their or the that these are small in condom use with partners as can the risk of STD infection. incident STDs should not be the for self-reports of condom use. in populations with high STD incidence (i.e., to the of persons who do not use condoms and do not an STD is used as the only measure of incorrect or condom use, of individuals as will Although most that failure to use a condom and does not always to the of an some have argued that the of an incident STD is a that there was incorrect or condom use. the of using diagnostic tests with 100% sensitivity (i.e., failure to and the of failures can result is what to be STDs. Thus, even persons who sex or who use condoms and (e.g., during the past 2 months) may to have a or incident infection. How Behavioral and Biologic Measures be Used in HIV and STD Prevention The effectiveness of an intervention to reduce HIV transmission possible, be on both behavioral and biologic Although it is always appropriate to behavioral measures, this may not be true for biologic For example, STD outcome measures may be for the and of behavior-change (e.g., I and or when are designed for prevention in populations with low STD prevalence (e.g., prevention biologic markers in these will the and complexity of these studies yielding Are In the of the of or on STD and HIV Given the complexity of the among behaviors, STDs, HIV, and the utility of biologic outcome measures in some settings, it has been that mathematical models be used to provide of the impact of behavior change in STD on HIV. of can be used to the focus of and to make about their public health Although the among behaviors, STDs, and HIV are a simple that of the is The number is a measure of the potential for of an at the when there are persons. This measure is as the number of infections by individual in an population. The of this number are the transmission sex the of change and the mean of such = to this a percentage change in of these three will have the impact on the of the of the on the time during which the infections in are the infection the population is no longer and the number of infections by person is a measure of the potential for a and in will reduce the of an The risk of infection for a person the of infection, which is a of and the prevalence of infection in Thus, if there is infection the partner the number of partners and the transmission should reduce the risk of infection. The complexity of the has to be when of impact behavior change or in STD incidence. have many different including a range of and of sex there must be a transmission sex and the of transmission will with the number of sex as a a low transmission sex and a high number of this is a Thus, the transmission will be a of the transmission and the number of unprotected such However, the transmission sex is to both and between This to be true for HIV, where some have a high transmission sex and others have a low transmission sex use in the will have a impact than use in the condoms used in in which partner is more to be will have a The impact of condom use on individual risk and this to risk depend on these nonlinear The relationship between a given in of the (i.e., partner change or partner transmission condom use or by STDs the and the incidence or prevalence of HIV will depend on the other important For populations in which there a percentage of a change in may have a small However, the = the change in would have a Because there is in sexual-risk behavior, the prevalence of a given STD will in a limited of the population. However, the prevalence of an infection will on (i.e., transmission and of and the of of sexual partners the population. is no simple relationship between the of different STDs, including HIV. Thus, in an intervention will models cannot provide with by for under conditions of help to identify the of these and suggest for future can also be used to of the of more widely in the The of models are and can be by using sensitivity can a useful but they are a rather than a studies of the impact of Although we have only two for different in have been developed and can often each should to be developed so that they and models should be to further empirical the impact of more is and data are models can be better and the reliability of the can be so that these models may a role in the future assessment of What to to to These of more appropriate measures of social desirability that have with the of a of populations. the of self-reports of behavior in (e.g., tend to sexual whereas tend to sexual a set of questions with appropriate that can be used to assess an risk behaviors. questions and formats that can be used for different and that recall to accuracy. the impact of using different to accurately the different patterns of risk issues of accuracy and truthfulness of self-report measures populations and their relationship to the of the impact on accuracy when using studies of of (e.g., use of and for research used in other than sexual behavior where there is a and develop to these sexual behavior methods to assess correct and consistent condom use. different data collection formats (e.g., other and their impact on responses. STD and HIV the relationship between STDs and the of HIV. more and more STD and HIV diagnostic among behavior, STDs, and the difference between individual and aggregate among different behaviors, of and correct and consistent condom use. of better data on which to verify models of HIV and STD further studies of the relationship between behaviors and STD and HIV incidence to and models of the effectiveness of better and methods to in the of more to public health (e.g., would be the impact on the if an intervention was widely adopted in a public health