The regression analysis used weighted least squares models and pooled data across all four sites. Each regression model included a series of binary variables reflecting the interaction between program site and program status (program or control group). The site-specific estimate is obtained from the regression simply from the difference between the binary variables corresponding to that site's program and control groups. The pooled impact estimate for a given outcome is obtained from the average of these four program-control differences. The weights used in the regressions accounted for the variability in the probability of selection to the program or control groups as well as for youth who did not complete the final follow-up survey.(2) Standard errors from the models were calculated taking into account the variability associated with these weights.
In addition to these variables, the regression models included a large number of variables to control for individual demographic and background characteristics measured from the baseline survey (Table III.4). For the small fraction of the sample who did not complete a baseline survey (fewer than 5 percent), a supplemental survey was administered at the next survey to collect key demographic information such as age, gender, and race/ethnicity. For other covariates, missing data were imputed using the mean for the sample in a given program site.
|Demographics and Background Characteristics
Date of interview
Responded to previous surveys
Presence of mother figure
Presence of father figure
|Baseline Contextual Factors
Communication with parents
Unmarried sister got pregnant
Sibling dropped out of school
|Baseline Measures of Behaviors and
Potential Mediators of Teen Sex
Perceived consequences of sex
Views on abstinence
Ability to resist pressure for sex
Expectations to have sex
Knowledge of STDs
Along with site-level results, the report presents estimated impacts on behavioral outcomes for several subgroups of potential interest.(3) Among these are subgroups defined by gender and several measures that might be linked to eventual behavior, such as baseline support for abstinence, religiosity, marital status of parents, and television viewing. All of these subgroups were defined from survey data collected at baseline, prior to any potential influence of the programs. A final subgroup, enrollment cohort, is also investigated because of important variation found across cohorts in an earlier DHHS study report (Maynard et al. 2005). The first of these subgroups includes youth enrolled in the 1999-2000 or the 2000-2001 cohorts; the second includes youth enrolled in the final, 2001-2002 cohort.
Impacts were estimated for one subgroup at time, following nearly the same methods as described above for the full sample. The only difference with these methods is that explanatory terms were added to the regression models reflecting the interaction between a given subgroup of interest (for example, gender) and each of the site dummies and the "site by treatment" interaction terms. Estimates for a given subgroup were then computed using the coefficients on these terms, following the same procedure described above.