Health Education Research Advance Access originally published online on November 22, 2005
Health Education Research 2006 21(4):441-451; doi:10.1093/her/cyh070
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AIDS education for Tanzanian youth: a mediation analysis
1 School of Public Health, University of Minnesota, 1300 South Second Street, Suite 300, Minneapolis, MN 55454, USA
2 Institute of Public Health, Muhimbili University College of Health Sciences, Dar Es Salaam, Tanzania
3 Institute for Nutrition Research, University of Oslo, Oslo, Norway
*Correspondence to: M. H. Stigler. E-mail: stigler{at}epi.umn.edu
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Abstract |
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Mediation analysis is a statistical technique that can be used to identify mechanisms by which intervention programs achieve their effects. This paper presents the results of a mediation analysis of Ngao, an acquired immunodeficiency syndrome (AIDS) education program that was implemented with school children in Grades 6 and 7 in Tanzania in the mid-1990s and evaluated using a controlled, group-randomized trial. The study examined which variables mediated the effect Ngao had in regard to (i) fostering positive attitudes towards people living with AIDS and (ii) decreasing intentions to be sexually active in the near future. Data from students who participated in a baseline and 12-month follow-up survey (n = 814) were analyzed. Results indicate that increasing exposure to AIDS information and increasing knowledge about human immunodeficiency virus transmission/prevention were significant mediators of the intervention's effect on alleviating the stigma associated with people living with AIDS. Moreover, encouraging more restrictive social norms about sexual intercourse was a significant mediator of the intervention's effect on decreasing students' intentions to be sexually active in the near future. Implications for future AIDS education programs for school children in this part of Africa designed to achieve similar goals are discussed.
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Introduction |
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At the start of the third decade of acquired immunodeficiency syndrome (AIDS), the World Health Organization estimates that 39.4 million people worldwide currently live with human immunodeficiency virus (HIV)/AIDS (UNAIDS, 2004). Of that, 11.8 million are between 15 and 24 years [1]. Among the new infections each year, >50% occur in this age group, of which only a fraction know they are infected [2]. In Tanzania, nearly one-third of all HIV/AIDS cases are among people aged 15–24 years [2]. In this age group, the estimated prevalence of HIV infection was 7.6% in 2001 [3].
While the rates of infection are startling, there is hope, especially in countries most affected by this epidemic. Prevention programs targeting young people in regions where AIDS and HIV infection are prevalent are contributing to increased knowledge about how HIV is transmitted, increased intentions to use condoms and delayed onset of sexual debut [2]. One example of a successful prevention program for young people living in regions like these is Ngao—an HIV/AIDS education program for students in sixth and seventh grades that was implemented and subsequently evaluated in primary schools in northeastern Tanzania in the mid-1990s. The overall goal of the program was to alleviate the consequences of HIV/AIDS in this region by decreasing student risk of HIV infection and reducing stigma attached to AIDS [4].
A randomized, controlled, multiple-community trial of Ngao demonstrated that it was reasonably successful in both regards. Twelve months after its implementation, students who had participated in Ngao reported significantly more positive attitudes towards people with AIDS (P < 0.01) [4]. Ngao participants also reported fewer intentions to engage in sexual intercourse (P < 0.01), and there was a trend that indicated that fewer students in the intervention schools had had their sexual debut during the previous year as compared with students in the control schools (7 versus 17%), though this was not statistically significant (P = 0.19) [4]. The results of this and other evaluations [5, 6] showed that AIDS education with school children in Tanzania was feasible and potentially efficacious.
The great burden of this pandemic requires widespread dissemination of effective prevention strategies to curb the spread of HIV infection [2]. Without knowing the mechanisms by which these programs work, however, the possibility of improving upon them remains limited. One method that can be used to assess the processes by which an intervention achieves its intended effects is mediation analysis [7]. Mediation analysis identifies which intermediate variables (or potential ‘mediators’) are responsible for an intervention's effect [7]. Most interventions are designed to change intermediate (or ‘mediating’) variables that are hypothesized to be causally related to the outcome of interest. These variables are called mediators when they account for (or explain) the relationship between exposure to the intervention and the outcome variable [8].
Mediation analysis tests theories underlying the development and implementation of interventions—namely, conceptual theory and action theory [9]. Conceptual theory provides the basis for the intervention design—it is the theory, driven in large part by etiologic research, that connects variables like social-cognitive factors (e.g. social norms) to the outcome of interest (e.g. intentions to have sex) [10]. Action theory identifies the strategies an intervention uses to achieve its effects—it is the theory that links program activities (e.g. small group discussions) to the mediating variables (e.g. social norms) they are meant to change [10]. Figure 1 illustrates ‘action theory’ and ‘conceptual theory’ in mediation.
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Four steps akin to a series of path analyses are followed in a mediation analysis [7]. Briefly, these include statistical tests of (i) the intervention's effect on the outcome variable; (ii) the intervention's effect on the potential mediator (which is a test of the intervention's action theory); (iii) the effect of the potential mediator on the outcome variable, after controlling for the effect of the intervention (which is a test of the conceptual theory) and (iv) the mediated effect, or the indirect path from the intervention to the potential mediator to the outcome (which provides a simultaneous test of the intervention's action theory and conceptual theory) [7].
Mediation analysis is useful because it can be used to separate elements of an intervention that are—and are not—critical to its success. If ineffective and effective intervention elements can be identified and eliminated or expanded, respectively, a particular education program could ultimately cost less and provide a greater benefit [7, 11]. This feature is particularly appealing in this context, given the scarce resources available for HIV prevention in sub-Saharan Africa. While mediation analysis is being utilized more frequently [12–18] (MacKinnon et al., 1993), no mediation analysis of an HIV/AIDS intervention for youth in Africa has been published to date. To help address this gap in knowledge, this paper presents the results of a mediation analysis of Ngao. Specifically, it examines how this AIDS education program achieved its effects in regard to (i) changing students' attitudes about people with AIDS and (ii) reducing students' intentions to engage in sexual activity in the future.
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Methods |
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Study design
This study is a secondary analysis of the data collected to evaluate the efficacy of Ngao. The original study was a nested cohort, group-randomized trial. All public primary (Grades 1–7) schools in the Arusha and Kilimanjaro regions of northeastern Tanzania were enumerated and stratified according to location (urban, semi-urban or rural). Three schools from each stratum in each region were randomly selected to participate. No schools refused participation. Of the 18 schools, one from each stratum in each region was randomly assigned to receive the Ngao intervention (n = 6), while the remaining (n = 12) served as a delayed-program control group that received Ngao after the final follow-up survey. Ethical clearances were obtained from the National AIDS Control Program, Ministry of Health, United Republic of Tanzania. Both passive parental consent and active student assent were required and obtained by researchers.
Participants
All students who were in the sixth grade in the 18 schools when the study began were invited to participate in the baseline (March 1992) and follow-up (March 1993) surveys. A total of 1063 sixth-grade students participated in the survey at baseline, representing 
85% of the eligible population. Non-participants were those students who were absent from school on the day of the survey. A total of 1074 seventh-grade students participated in the survey at follow-up; of these, 814 (77%) also participated at baseline. The current study is based on this cohort of 814 students, 258 of whom were in the intervention condition and 556 of whom served as a comparison. This sample of analysis was chosen to be consistent with previously published studies of Ngao [4]. Participants and non-participants did not differ on important sociodemographic variables, as reported previously (see [4]).
Intervention
Tanzanian health educators in collaboration with investigators from the Center for International Health at the University of Bergen, Norway, developed this school-based HIV/AIDS education program for young people. The program is aptly named Ngao (‘shield’ in Kiswahili, the national language used in Tanzania and a common language used throughout East Africa) to symbolize that students can learn to protect themselves from HIV. The overall goals of the program were (i) to alleviate the consequences of HIV infection and AIDS in the community by reducing the stigma attached to AIDS and (ii) to reduce students' risk of HIV infection by delaying initiation of sexual activity. A teacher's manual and a booklet for students to take home were produced in Kiswahili. Two teachers and one health worker from each school were trained to implement the program, which was executed over a 2- to 3-month period, averaging 25–30 hours in total. Specific program activities and objectives are described in Table I, with examples of subjects addressed in particular activities. Given the diversity of cultural and ethnic backgrounds in this area of Tanzania, teachers were allowed to tailor activities to fit the specific norms and values of each community, though few (if any) adaptations occurred during implementation [6]. The program's theoretical framework (see intervention objectives, Table I) was guided by constructs from the Theory of Reasoned Action [19, 20] and Social Learning Theory [21]. Further details about the program activities are published elsewhere, along with the results of a process evaluation study [6]. As there were strong objections from the Ministry of Education and Culture at that time regarding providing information about condom use in primary schools in Tanzania, only an optional section about condom use was provided, so that teachers who felt it was appropriate or who received direction questions about condom use from students would know how to address the issue appropriately. None of the teachers reported using this particular section of the intervention program, though [6].
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Measures
The survey was designed based on the World Health Organization's knowledge, attitudes, beliefs and practices survey for adolescents [22] and underwent a pilot study [23] before being revised and then subsequently used in the study presented here. Trained project staff from Tanzania administered the surveys, which were conducted in the classrooms with no teachers present. These staff assured students that their answers would be kept strictly confidential. None of the students present at the time of the survey refused to participate, either at baseline or at follow-up. Students absent from school on the day of the survey were not contacted for make-ups due to the remote location of several schools and lack of resources [5].
Multi-item summative scales were created to measure most constructs of interest in this study, though for one measure an individual item was used. For the purposes of this mediation analysis, two outcome variables and eight potential mediating variables were selected. The two outcome variables are consistent with the primary goals of this education program and the positive effects that were achieved 12 months after its implementation [4]. The eight mediating variables correspond to the objectives of Ngao and/or conceptual theory upon which it is based [4]. A description of the variables used to measure these constructs, including a measure of internal consistency (Cronbach's 
) from the baseline survey, is provided in Table II. Students also provided demographic information on the survey, like gender and grade.
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The two outcome variables were (i) attitudes towards people with AIDS (high score meaning more positive attitudes towards people with AIDS) and (ii) intentions to have sexual intercourse in the near future (high score meaning stronger intentions to have sexual intercourse; 1 = ‘No’, 2 = ‘I don't know’, 3 = ‘Yes, maybe’, 4 = ‘Yes, I am sure’). The eight mediating variables included (i) exposure to AIDS information (high score meaning higher levels of information exposure), (ii) communication about HIV/AIDS (high score meaning higher levels of communication), (iii) AIDS knowledge (high score meaning more correct knowledge about HIV/AIDS), (iv) perceived susceptibility to HIV/AIDS (high score meaning low susceptibility to HIV/AIDS), (v) perceived severity of HIV/AIDS (high score meaning low perceived severity to HIV/AIDS), (vi) subjective norms regarding sexual activity (high score meaning more restrictive norms about sexual activity), (vii) attitudes about sexual activity (high score meaning more restrictive attitudes about sexual activity) and (viii) self-efficacy in regard to sexual activity (high score meaning less confidence in their ability to refuse offers of sexual intercourse). The analysis strategy employed in this study (described below) assumes that variables are normally distributed. All of the measures described were, except for perceived severity of HIV/AIDS (skewness > 2 and/or kurtosis > 7), so this was log transformed before use.
Analysis
Mediation analyses were conducted on the follow-up survey using the rationale and statistical procedures outlined by MacKinnon and his colleagues [7, 24–26]. Briefly, an effect was said to be mediated if (i) the intervention had a statistically significant effect on the hypothesized mediator (), (ii) the hypothesized mediator was associated with the outcome of interest (ß) after controlling for the intervention effect and (iii) the mediated effect (ß) was statistically significant [26] (see Fig. 1). The estimate of the mediated effect was calculated as the product (ß) of the path between the intervention and the hypothesized mediator () and the path between the hypothesized mediator and the outcome variable (ß) (see Fig. 1). The standard error of the estimate was calculated using the multivariate delta method based on a first-order Taylor series expansion 
[27]. The statistical test of the mediated effect (ß/
ß) was evaluated using an empirically derived distribution of critical values (z'), for which 0.97 is the critical value for the 0.05 significance level. This method is recommended over other tests when both and ß are non-zero, as it has the greatest power to detect a significant intervening variable effect while maintaining the appropriate Type I error rates [26]. Mixed-effects regression models were used to appropriately account for the multi-level nature of this data set (i.e. school was treated as a nested random effect) [24].
All statistical models employed in these analyses were adjusted for a common set of covariates, namely, the baseline measure of the dependent variable, baseline measures of the hypothesized mediators and gender. There were no significant differences in Ngao's effect on the potential mediators or outcomes of interest in this study by gender (i.e. gender was not an effect modifier), so the mediation analysis was conducted on the entire sample, not stratified by gender. Gender, however, was considered as a possible confounder, and therefore adjusted for in these regression models, since differences do exist between boys and girls in several variables considered here (e.g. boys did report more sexual activity than girls) [4]. Regression models were blocked by six strata to account for the study design—that is, the main effects and interactions of region (Arusha/Kilimanjaro) and location (urban/semi-urban/rural) were included, too.
Analyses included single-mediator (i.e. the effect of each potential mediator on each outcome was assessed individually) and multiple-mediator models (i.e. the effects of a set of potential mediators on each outcome were assessed simultaneously). Multiple-mediator models included only potential mediators that were statistically significant in single-mediator models. Contrasts were performed in the multiple-mediator models to determine if effects were significantly different from one another [25]. Finally, the percentage of the intervention effect mediated by a particular (set of) variable(s) was calculated as the estimate of the mediated effect (ß) divided by the total effect of the intervention (
or ß + ') [7, 26].
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Results |
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Table III presents the results of the mediation analysis in regard to the students' attitudes towards people with AIDS. Although all the potential mediating variables were significantly associated with this outcome (see ß), Ngao changed only a subset of them (see
). In the single-mediator models (which examined each potential mediator by itself—see ß), statistically significant mediators included communication about HIV/AIDS, exposure to HIV/AIDS information, knowledge about HIV/AIDS and subjective norms about sexual activity. In a multiple-mediator model (which examined these four significant mediators simultaneously—see ß), only exposure to HIV/AIDS information and knowledge about HIV/AIDS remained significant. A contrast test showed that these two mediators were not statistically significantly different from one another [difference = 0.199; 95% confidence interval = (–0.244, 0.642)], indicating that they were equally important mediators of Ngao's effect on this outcome. Together, the two variables accounted for 38% of Ngao's effect on attitudes towards people with AIDS.
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Table IV presents the results of the mediation analysis on adolescents' intentions to have sexual intercourse in the near future. Among the potential mediators considered, only three were significantly associated with this outcome (see ß): (i) subjective norms about sexual activity, (ii) attitudes about sexual activity and (iii) self-efficacy in regard to sexual activity—among these, Ngao only had a significant effect on subjective norms about sexual activity (see
). Moreover, subjective norm was a statistically significant mediator of the intervention's effect (see ß). Changes in this variable accounted for 16% of Ngao's effect on intentions to have sexual intercourse in the next 3 months.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionAcknowledgementsReferences |
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Mediation analysis is useful in prevention research because it can help separate out the elements of an intervention that are—and are not—critical to its success. This paper presents the results of a mediation analysis of Ngao, an AIDS education program for sixth and seventh grade students in Tanzania. To the best of our knowledge, it is the first to report on a mediation analysis of an HIV/AIDS program for school children in Africa. The present analyses were able to identify some of the mechanisms through which this AIDS education program appears to have achieved its effects—but not all. A discussion of these mediating mechanisms, organized according to Ngao's primary goals, follows.
One goal of Ngao was to reduce the stigma associated with HIV/AIDS. In this study, this goal was operationalized in terms of reducing students' negative attitudes towards people living with AIDS. The results of these mediation analyses suggest that intervention-related changes in exposure to HIV/AIDS information and knowledge of HIV/AIDS were critical in terms of the intervention's effect on ‘this’ outcome. As noted in Table I, Ngao sought to increase exposure to HIV/AIDS information and, in turn, increase student's knowledge (and/or correct misinformation) about HIV/AIDS using activities like didactic lectures in the classroom, creating/displaying posters at school and writing/performing poetry and songs at school. These activities addressed topics like how HIV is and is not transmitted and how people can adequately protect themselves from becoming infected, and introduced ways in which one can interact with and support those living with HIV/AIDS. The results of this study suggest that program developers wishing to design interventions to reduce HIV/AIDS-related stigma should consider including objectives like these in their program (i.e. increasing exposure to information about HIV/AIDS and increasing knowledge about HIV/AIDS). Further, they may find it helpful to use similar activities (e.g. lectures) that cover related topics. Reducing HIV/AIDS-related stigma and discrimination is becoming an increasingly important outcome to consider in the context of intervention, especially in settings like these, since AIDS-related stigma remains a significant barrier to preventing further infection and alleviating the impact of AIDS worldwide [28, 29]. More efficacious interventions are needed to address this problem.
The second goal of Ngao was to limit the risk of HIV infection by decreasing one's intentions to have sexual intercourse in the future. The only significant mediator of the intervention's effect on this outcome was a change in subjective norms in regard to sexual activity—fostering more restrictive social norms about sexual activity mediated the decrease in behavioral intentions to engage in sexual intercourse. As noted in Table I, Ngao tried to encourage more restrictive social norms about sexual activity through small group discussions in the classroom. Discussions were sometimes facilitated by trained peer leaders, students who were elected by their classmates as colleagues who were particularly respected and admired. During these meetings, students talked about how they felt about people their age being sexually active—whether it was appropriate, safe and acceptable or not—and what other people in their community (e.g. parents, teachers, elders) thought about young people being sexually active. Group discussions were held separately for boys and girls, when appropriate, to ease comfort levels and encourage as much participation in discussion as possible. Activities like these may be useful to program developers. Changing social norms appears to be important in the context of interventions designed to reduce students' intentions to be sexually active.
The results of this part of the study (i.e. investigating mechanisms of intervention responsible for decreasing intentions to engage in sexual activity in the future) parallel mediation analyses that have been conducted on other kinds of prevention programs for young people, like drug education programs in the United States. Changing social norms has been a consistent, significant mediator of many drug education programs' effects on behavioral outcomes like alcohol, tobacco and marijuana use [30]. This approach may be relevant to HIV prevention programs for youth as well, given the importance of the social environment to young people and the critical role interpersonal and social factors have had in the spread of the HIV/AIDS epidemic [31, 32]. A normative approach to AIDS education could potentially address misperceptions in social norms about sexual activity (e.g. increasing students' awareness that the majority of their peers are ‘not’ having sex—as many young people incorrectly perceive that ‘everybody is doing it’); the social acceptability of early sexual debut so that friends, parents, teachers and elders in the community are less tolerant of early sexual activity and students' motivation to comply with healthier social norms.
Mediation analyses of other HIV prevention programs for adult populations in the United States appear to have achieved their effects through changes in self-efficacy and attitudes, but not through changes in social norms [13–15]. These two programs (Project RESPECT and the WINGS Project) were more skill-based than Ngao and focused primarily on increasing the consistent use of condoms using clinic-based intervention. As noted previously, the primary goals of Ngao did not include a focus on increasing condom use among youth, given restrictions placed on the intervention by the Ministry of Culture and Education [6]. The only strategy that Ngao used to increase self-efficacy was role-plays. Alone, these did not produce the desired intervention effect, suggesting that more (or different kinds of) skills training components would have been a helpful addition to the program (since self-efficacy was related to intentions to engage in sexual activity; ß in Table IV). Changes in attitudes about sexual activity may have been difficult to achieve on average in this part of Tanzania, given diversity in cultural and ethnic backgrounds; at the follow-up survey, there was still a great deal of variability between individuals in this construct [4]. The intervention's effect could have been enhanced by changes in attitudes, too (since attitudes were related to intentions, see ß in Table IV).
While increasing exposure to HIV/AIDS information, correcting knowledge about HIV/AIDS and changing subjective norms about sexual activity appear to have been critical components of Ngao, changes in these mediators accounted for only a portion of the total effect Ngao had on the two outcomes (38 and 16%, for intervention-related changes in HIV-related stigma and intentions to engage in sexual activity, respectively). Some of the missing effects could be due to measurement error, as some of the measures of potential mediators used in this study were not particularly reliable [7]. Alternatively, an unmeasured mediators may be responsible for these effects.
The most important limitation of this study is the following. Although all of the regression models were adjusted for the baseline values of the mediator and outcome variables, the analysis of the mediating process (ß) was essentially cross-sectional—in this study, mediators did not precede outcome variables in time. Mediating processes likely unfold over time—though not instantaneous, they may be rapid [33]. Although surveys were conducted at a 6-month follow-up point, student identities could only be linked between baseline and 12-month follow-up, due to constraints imposed during data collection. These analyses, therefore, represent the mechanisms of change associated with Ngao at one point in time, 12 months after implementation.
Despite this limitation, this study should provide some initial evidence regarding how AIDS education programs might work—or not work—among school students in this region of Africa. The lack of attention to mediating processes of interventions is a serious limitation of prior AIDS research in Africa. More research is needed to refine the conceptual and action theories used to help guide the development of programs that seek to prevent HIV infection among young people and reduce the stigma associated with HIV and AIDS in these communities. This is particularly critical in Africa where the HIV epidemic is challenging and youth are increasingly affected [1].
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Acknowledgements |
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The original study of Ngao was supported by a grant from the Norwegian Agency for Development and Cooperation and by the Tanzanian Ministry of Health. This work was funded in part by a grant from the Norwegian Council of Universities' Programme for Development Research and Education and facilitated by the following collaborating institutions: Muhimbili University College of Health Sciences, Kilimanjaro Christian Medical College, Centre for Educational Development in Health Arusha in Tanzania, the School of Public Health at the University of Minnesota and the Universities of Oslo and Bergen, Norway.
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Received on December 7, 2004; accepted on October 26, 2005
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