98%: Is misinformation being spread about a review of trans youth medicine?

Episode Summary

Executive Summary: The episode examines a viral claim that the Cass Review on youth gender identity services ignored 98% of evidence. It explains that this is false: systematic reviews assessed all available studies, included moderate-quality research, and excluded low-quality studies from conclusions. The real issue was the weak evidence base and lack of long-term follow-up.

Main Topics: The Cass Review and its findings (Priority: 5/5): The review of England’s gender identity services for children concluded that the evidence for medical interventions was weak and that young people had been let down by poor-quality research. The '98% of evidence ignored' claim (Priority: 5/5): A viral social media claim alleged the review dismissed 98% of evidence, but the episode shows this came from a misunderstanding of how the studies were categorized. How systematic reviews work (Priority: 5/5): Experts explain that all studies were evaluated, with quality assessed using standard research methods; low-quality studies were removed from the final analysis, while moderate-quality studies were still included. Why randomised controlled trials were not used (Priority: 4/5): The segment addresses criticism that only double-blind randomised trials were acceptable, clarifying that none existed and that such blinding is often impossible in this medical context. The evidence base for puberty blockers and hormones (Priority: 5/5): Researchers found the main weakness was not simply the absence of randomised trials, but the lack of long-term follow-up and overall poor study quality. Disinformation and public interpretation (Priority: 4/5): The discussion traces the false 98% claim to a BMJ press release summary and social media math, showing how omitted nuance fueled misinformation.

Key Arguments: The Cass Review did not ignore 98% of evidence; it evaluated all available studies and used standard quality criteria to decide which evidence could support conclusions. Only two studies across the reviews were judged high quality, but many moderate-quality studies were still included in the synthesis. Low-quality studies were excluded because weak or unclear methods could produce unreliable or skewed results. Randomised double-blind trials were not feasible in this area because patients would know whether they were taking puberty blockers or hormones. The core problem identified by the review was not just study design, but the lack of long-term follow-up on outcomes and harms. The public claim arose from a simplified reading of a BMJ press release that mentioned only the high-quality studies and omitted the moderate-quality evidence. Cass argues that using weak evidence for this group would mean applying a lower standard of care than for other children. Misinformation about the review, in Cass’s view, risks harming young people and undermining informed medical decision-making.

Data Points: Scientific papers analyzed: 103 - Across two systematic reviews: one on puberty blockers and one on hormone treatments. High-quality studies: 2 - Only two studies were deemed high quality across the reviews. Percentage high quality: 2% - Derived from 2 of 103 studies being high quality. Percentage not high quality: 98% - Represents studies not classified as high quality, but not studies ignored. Studies included in synthesis: nearly 60% - Moderate-quality studies were included in the final synthesis. Low-quality studies: around 40% - These were not used to form conclusions because methods were too weak or unclear. High-quality studies in one review: 1 of 53 - Referenced in the BMJ press release for one review. High-quality studies in the other review: 1 of 50 - Referenced in the BMJ press release for the second review. Moderate-quality studies in hormone review: 34 - Included in the systematic review of hormone treatment evidence. Moderate-quality studies in puberty blocker review: 26 - Included in the systematic review of puberty blocker evidence.

Pivotal Quotes: "We didn't identify any randomised control trials, but we had non-randomised studies." — Professor Catherine Hewitt: Explaining why the York team used a different quality-assessment tool instead of RCT criteria. "The biggest weakness was that they just didn't follow young people through for long enough for us to really understand the long-term outcomes." — Dr Hilary Cass: Summarizing the main limitation of the evidence base used in the review. "Adults who deliberately spread misinformation about this topic are putting young people at risk." — Dr Hilary Cass: Her response to criticism and misinformation surrounding the review.

Implications: The episode warns listeners to distinguish between 'not high quality' and 'not used at all.' For clinicians and the public, it underscores that evidence on youth gender treatments remains limited, making careful interpretation and better research essential.