Studies › Methodology · Last reviewed 2026-05-16
Methodological criticism
Summary
Peer-reviewed criticism of the Dutch evidence base focuses on three points: (1) the absence of control groups and randomisation, (2) selective attrition and validity of measurement instruments in the de Vries 2014 cohort, and (3) limited generalisability to later referral populations with different demographic profiles. The main authors are Biggs (2022, 2023), Levine et al. (2022) and Abbruzzese et al. (2023).
1. Michael Biggs (Oxford, 2022 / 2023)
Biggs published in 2022 a detailed re-evaluation of de Vries 2011 and de Vries 2014 in Journal of Sex & Marital Therapy.1 Main points:
- The effect size on psychological functioning is partly determined by a single participant.
- The UGDS uses different wordings for MtF and FtM, which complicates T0/T2 comparison.
- Attrition was not at-random; poorer-functioning patients are potentially under-represented at T2.
See also /evaluations/biggs-puberty-blocker-overview/ for his full publication overview.
2. Stephen Levine, E. Abbruzzese, Julia Mason (2022)
In Journal of Sex & Marital Therapy, Levine, Abbruzzese and Mason argue that the informed-consent structure of the Dutch Protocol is not adequate for decision-making about irreversible interventions in minors, given incomplete knowledge of long-term effects.2 Their full work is summarised at /evaluations/levine-critiques/.
3. Abbruzzese, Levine, Mason (2023) — "Generalisability"
In a follow-up article the authors argue that the original Dutch population — early-onset, not subject to ROGD patterns, without pronounced ASD comorbidity — differs substantially from the contemporary population in international clinics. Applying the protocol to that other population, according to the authors, has reduced its external validity.3
4. Bewley, Cass and the NICE reviews
The systematic reviews of NICE (2020) and the Cass Review (2024) classify the evidence as "very low certainty" per GRADE; this judgement was also endorsed in 2020 in The BMJ by Susan Bewley et al. in a column on informed consent in adolescents.4
See also
- Criticised studies: de Vries 2011, de Vries 2014
- Specific criticism per author: Biggs, Levine et al.
- Attrition analysis: Sample size and attrition
- Replication problems: Replication attempts
- Systematic evaluations: Cass Review, SBU
- Broader debate: Scientific criticism
- People register — Biggs, Levine, Abbruzzese, Mason, Bewley.
- Timeline — criticism publications in chronology.
- Original publications — full bibliography.
- FAQ · Glossary.
Footnotes
- Biggs M. The Dutch Protocol for juvenile transsexuals: origins and evidence. J Sex Marital Ther. 2023;49(4):348–68.
- Levine SB, Abbruzzese E, Mason JW. Reconsidering informed consent for trans-identified children, adolescents, and young adults. J Sex Marital Ther. 2022;48(7):706–27.
- Abbruzzese E, Levine SB, Mason JW. The myth of "reliable research" in pediatric gender medicine. J Sex Marital Ther. 2023;49(6):673–99.
- Bewley S, McCartney M, Meads C, Rodgers A. Sex, gender and medical data. BMJ. 2021;372:n735.