University of York — Cass systematic reviews
The University of York is a British university. Its Centre for Reviews and Dissemination (CRD) specialises in systematic reviews of healthcare research.
The reviews
For the Cass Review, researchers from York conducted a series of systematic reviews. They cover the characteristics of referred young people, care pathways, international guidelines, social transition, puberty blockers and hormone treatment. The reviews were published after peer review in 2024 in the journal Archives of Disease in Childhood.
Why it is on this list
The reviews form the scientific basis of Cass's final report. The researchers found that the evidence for puberty blockers and hormones in minors is limited and of low quality. The methodology also came under criticism, including the way studies were assessed for quality. The link leads to the CRD's page; the articles themselves are published by the journal. See also science and debate.
The Centre for Reviews and Dissemination
The CRD is a research institute that brings together and assesses data from multiple studies, so that decisions about health, public health and social care can be based on research. Its work includes the evaluation of medical technologies, methodological development, children's health, mental health and public health. The institute manages PROSPERO, an international registry in which researchers preregister systematic reviews. According to the website, the registry contains more than 500,000 records.
Design and findings
There were seven reviews. They were published on 10 April 2024, at the same time as the final report. The researchers assessed the quality of studies using an adapted version of the Newcastle-Ottawa Scale and the Mixed Methods Appraisal Tool. They included only English-language studies involving minors and did not assess the certainty of the evidence for each outcome. The differences in evidentiary strength between types of research are explained in the evidence pyramid in gender care. For puberty blockers, they found 50 studies: one of high quality, 25 of moderate quality and 24 of low quality. For hormone treatment, there were 53 studies: one of high quality, 33 of moderate quality and 19 of low quality. Bone health appeared to lag during treatment with puberty blockers. No conclusion could be drawn about the effect on dysphoria and mental health. A planned study into the later outcomes of approximately 9,000 young people did not go ahead because the necessary cooperation was not forthcoming.
Criticism and defence
In July 2024, a group associated with Yale Law School wrote that the reviews had serious shortcomings; see the article on the Yale report against the Cass Review. In May 2025, an article by Noone and colleagues in BMC Medical Research Methodology used the ROBIS tool to identify a high risk of bias. By contrast, a May 2026 review by the British Medical Association deemed the methodology sound. More explanation is provided in systematic reviews.