{ "background": "Community health centres are pivotal for public health delivery in Tanzania, yet rigorous methodological evaluations of their impact on health risk reduction are limited. The difference-in-differences (DiD) model is a prominent quasi-experimental technique for causal inference in such settings, but its application and methodological rigour in this specific context have not been systematically appraised.", "purpose and objectives": "This systematic review aims to critically evaluate the application of the DiD model in assessing risk reduction outcomes within Tanzanian community health centre systems, focusing on its methodological execution, assumptions, and reporting standards.", "methodology": "A systematic search of multiple academic databases was conducted following PRISMA guidelines. Eligible studies employed a DiD design to evaluate health interventions in Tanzanian community health centres. Studies were screened, selected, and their methodological quality assessed using a predefined checklist focusing on DiD assumptions, model specification, and robustness checks. The canonical two-way fixed effects model is $Y{it} = \\alpha + \\beta (Treati \\times Postt) + \\gammai + \\deltat + \\epsilon{it}$.", "findings": "Of the 18 studies meeting inclusion criteria, only 33% adequately tested the parallel trends assumption, a fundamental prerequisite for DiD validity. A predominant theme was the frequent omission of key robustness checks, such as placebo tests or the use of clustered standard errors to account for intra-clinic correlation. Reported treatment effects often lacked accompanying measures of statistical uncertainty, such as 95% confidence intervals.", "conclusion": "The application of the DiD model in this field is often methodologically incomplete, potentially compromising the reliability of estimated intervention effects on health risks. This undermines evidence-based policy decisions aimed at strengthening community health systems.", "recommendations": "Future research must rigorously test and report on DiD assumptions, incorporate robustness analyses, and explicitly quantify uncertainty. Journal editors and peer reviewers should enforce stricter methodological reporting standards for quasi-experimental studies in health systems research.", "key words":