Extending TTM-Based Quantitative Predictions to HIV Prevention Among MSM

The purpose of this study was to extend the Testing Theory-based Quantitative Predictions approach (TTQP) using the transtheoretical model of behavior change (TTM) to condom use behavior in a sample of men who have sex with men (MSM). The TTQP approach employs the theory to generate effect size predictions, then the observed effect sizes can be calculated and compared to the predicted effect sizes. The effect size predictions in this study were made: 1) based on the omega squared reported in previous TTQP studies of other health behavior changes (e.g., smoking cessation); 2) based on theoretical considerations; and 3) calculated from the data reported in previous TTM condom use studies. The study design was a secondary analysis using data from a cross-sectional study. The final sample size was 185. However, the number of participants who were limited to membership in the first three stages (i.e., at-risk participants) was 85. The observed ω2 across the first three stages and their 90%, 95%, as well as 99% confidence intervals were calculated using SAS. Results demonstrated that when 90% CI was used, 4 of 10 predictions were confirmed for predictions based on previous TTQP studies of other health behavior changes, 8 of 17 predictions were confirmed for predictions based on theoretical considerations, and 13 of 16 predictions were confirmed for predictions based on previous TTM condom use studies; when 95% CI was used, 4 of 10 predictions were confirmed for predictions based on previous TTQP studies of other health behavior changes, 9 of 17 predictions were confirmed for predictions based on theoretical considerations, and 13 of 16 predictions were confirmed for predictions based on previous TTM condom use studies; when 99% CI was used, 6 of 10 predictions were confirmed for predictions based on previous TTQP studies of other health behavior changes, 14 of 17 predictions were confirmed for predictions based on theoretical considerations, and 15 of 16 predictions were confirmed for predictions based on previous TTM condom use studies. The explanations of failed predictions for this study included sample fluctuation (near misses), a need for prediction/theory revision, and a need for further recalibration of the effect size categories. Findings suggested that the first two prediction methods (i.e., predictions based on theoretical considerations and predictions based on previous TTQP studies of other health behavior changes) did not do well at predicting effect size estimates for MSM condom use behavior when 90% CI or 95% CI was used. However, the third prediction method (i.e., predictions calculated from the data reported in previous TTM condom use studies) did very well at predicting effect size estimates for MSM condom use behavior, no matter which CI was used. The inadequate fit of predictions based on previous studies of other health behavior changes and the good fit of predictions derived from previous TTM condom use studies indicated that TTM constructs for condom use have different effects across the first three stages of change compared to other health behavior changes (e.g., smoking, sun protection, or diet), and that future studies should use previous empirical data based on the same health behavior change to generate effect size predictions whenever possible. The present study provides empirical data for future research making TTM-based quantitative predictions to condom use behavior. Moreover, the present study supports the need to further calibrate the effect size categories and the need to revise theory using empirical data. Replication of this study using independent samples would be very helpful to refine theoretical predictions.