Critically appraising the Cass report: methodological flaws and unsupported claims

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