Re-analysis of health and educational impacts of a school-based deworming programme in western Kenya: a statistical replication of a cluster quasi-randomized stepped-wedge trial

Introduction: Helminth (worm) infections cause morbidity among poor communities worldwide. An influential study conducted in Kenya in 1998-99 reported that a school-based drug-and-educational intervention had benefits for worm infections and school attendance. Methods: In this statistical replication, we re-analysed data from this cluster quasi-randomized stepped-wedge trial, specifying two co-primary outcomes: school attendance and examination performance. We estimated intention-to-treat effects using year-stratified cluster-summary analysis and observation-level random-effects regression, and combined both years with a random-effects model accounting for year. The participants were not blinded to allocation status, and other interventions were concurrently conducted in a sub-set of schools. A protocol guiding outcome data collection was not available. Results: Quasi-randomization resulted in three similar groups of 25 schools. There was a substantial amount of missing data. In year-stratified cluster-summary analysis, there was no clear evidence for improvement in either school attendance or examination performance. In year-stratified regression models, there was some evidence of improvement in school attendance [adjusted odds ratios (aOR): year 1: 1.48, 95% confidence interval (CI) 0.88-2.52, P = 0.147; year 2: 1.23, 95% CI 1.01-1.51, P = 0.044], but not examination performance (adjusted differences: year 1: -0.135, 95% CI -0.323-0.054, P = 0.161; year 2: -0.017, 95% CI -0.201-0.166, P = 0.854). When both years were combined, there was strong evidence of an effect on attendance (aOR 1.82, 95% CI 1.74-1.91, P < 0.001), but not examination performance (adjusted difference -0.121, 95% CI -0.293-0.052, P = 0.169). Conclusions: The evidence supporting an improvement in school attendance differed by analysis method. This, and various other important limitations of the data, caution against over-interpretation of the results. We find that the study provides some evidence, but with high risk of bias, that a school-based drug-treatment and health-education intervention improved school attendance and no evidence of effect on examination performance.