Threshold of evidence needed for widespread implementation

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Overall, because of the potential ability of school-based interventions to be implemented broadly and to reach large proportions of young people, these interventions should require low-to-moderate thresholds of evidence before being recommended for widespread implementation. However, because the discussion of sexual activity, especially condom use, in schools may be controversial, the threshold varies somewhat according to the community, the grade level in which the intervention is designed to take place and the intervention's content, targeted behaviour and implementer. Conclusions made in this review are based on the consideration of these issues and thresholds (Table 5.2).

5.2.3 Review of studies

All studies were summarized in a template by one of this review's authors (BL) and then reviewed by a second author (DK). The summaries were then sent to the author of the original study for verification. Changes were made as appropriate. The complete version of these summaries is available on the web (

For this review, all reported outcomes (for example, effects on behaviour) were considered significant if they were statistically significant at the 0.05 level and this significance was based either on the total sample or a subsample that was roughly one third of the total sample or larger (for example, either males or females, youths younger or older than a certain age, or sexually experienced or sexually inexperienced youths). Some studies found significant effects for important subgroups but not for the entire sample.

Studies sometimes reported results for multiple measures of each behaviour, for different time periods, for different subgroups or for combinations of these. Thus, some studies reported only one or a small number of significant positive effects on behaviour as well as a large majority of results that were not significant. To avoid presenting only the positive results and to provide a more balanced overview, the following rules for summarizing results were adopted. First, for different measures of the same outcome behaviour: all measures across all the studies were rank-ordered according to their probable impact on prevalence. For example, the use of condoms over a long period of time was ranked higher than condom use at first sexual intercourse. Only the results from the highest ranked measure reported in each study were included in the tables. Second, because short-term effects on behaviour would have little impact on HIV prevalence, only those results reported for periods of 3 months or longer were included in the tables. In addition, because studies were not likely to have sufficient statistical power to measure the impact on those behaviours or outcomes that change slowly (that is, initiation of sex, pregnancy rates or rates of sexually transmitted infections [STIs]), only those results measuring impact on these outcomes for at least 6 months were included.

Table 5.2

Threshold of evidence needed to recommend widespread implementation of each type of intervention

Intervention type Criterion3 Overall Comments


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