Abstract
BACKGROUND: The Cass Review aimed to provide recommendations for the delivery of services for gender diverse children and young people in England. The final product of this project, the Cass report, relied on commissioned research output, including quantitative and qualitative primary research as well as seven systematic reviews, to inform its recommendations and conclusions. METHODS: We critically evaluated the Cass report and the research that was commissioned to inform it. To evaluate the Risk of Bias within the seven systematic reviews commissioned by the Cass Review, we applied the ROBIS tool - a domain-based assessment of risk of bias within systematic reviews. It focuses on four domains (i) study eligibility criteria, (ii) identification and selection of studies, (iii) data collection and study appraisal, and (iv) synthesis and findings. To maintain rigour, the ROBIS tool was applied to each systematic review by two independent assessors, within Covidence, with conflicts resolved by an additional two independent assessors. We also conducted a detailed critical evaluation of the methods used in the survey of gender services for young people in Europe, the two quantitative studies of health records, and the qualitative study on the experience of gender dysphoria among young people and the claims made in the Cass report based on these studies. RESULTS: Using the ROBIS tool, we identified a high risk of bias in each of the systematic reviews driven by unexplained protocol deviations, ambiguous eligibility criteria, inadequate study identification, and the failure to integrate consideration of these limitations into the conclusions derived from the evidence syntheses. We also identified methodological flaws and unsubstantiated claims in the primary research that suggest a double standard in the quality of evidence produced for the Cass report compared to quality appraisal in the systematic reviews. CONCLUSIONS: We discuss these issues in relation to how evidence regarding gender affirming care is framed, the wider political context, and the future for gender affirming care. The Cass report's recommendations, given its methodological flaws and misrepresentation of evidence, warrant critical scrutiny to ensure ethical and effective support for gender-diverse youth.