"Gender identity" is increasingly treated in policy, healthcare protocols, and legislation as a fixed, measurable fact — something that a questionnaire or intake interview can record just as reliably as height or blood pressure. A systematic review published in May 2026 in the journal Biomedical Engineering OnLine raises serious doubts about that assumption. The researchers, led by Nausheen Ahmad, examined which instruments exist worldwide for determining sex and gender, and how well those instruments actually perform. The findings offer little reassurance to anyone presenting gender identity as a robust, clinically useful concept.

What exactly the review examined

The team searched the scientific literature for instruments measuring sex and gender characteristics and found 34 across 46 studies: eight instruments measuring sex and 26 measuring gender. For each instrument, the researchers assessed its measurement properties according to established psychometric criteria — construct validity (whether the instrument actually measures what it claims to measure), test-retest reliability, and the extent to which the instrument has been validated in the populations for which it is used.

Only three of the 26 instruments scored highly

Of the 26 instruments specifically measuring gender, only three received a high-quality rating according to the review. The rest scored no higher than moderate or low on the measurement properties examined. It is also notable which property was most often missing: while construct validity was reported most frequently, test-retest reliability — whether an instrument produces the same result when administered a second time — was the property studied least often. An instrument that no one has checked for consistency over repeated administrations can hardly be considered a stable, clinically reliable measure.

Validation for non-binary people is almost entirely absent

The picture becomes even bleaker when the researchers look at populations outside the binary male-female framework. Of all the instruments examined, exactly one — the Gender Self Report — had also been validated among non-binary participants. For the dozens of other questionnaires and scales, it is unknown whether they meaningfully measure what they claim to measure in this group. The same criticism applies to the growing list of identity labels described in this site's catalogue of gender identities: the more fine-grained the classification, the harder it becomes to have a validated measurement instrument for each individual category. So while a label exists for a term such as non-binary, there is barely any substantiated way to determine what that label actually measures in an individual.

What this says about the concept itself

The authors of the review put it cautiously: further validation of the better-rated instruments in diverse samples is "timely" for fairer policy and practice. That wording is revealing in itself. A concept that, after decades of research, is still waiting for sound measurement instruments is not an established biological or psychological fact — it is a working hypothesis whose operationalisation still largely remains to be developed. This aligns with the broader conceptual criticism of gender identity: there is no objective marker, no blood test, no scan. Everything measured is based on self-report, and this review shows that even such self-reports are collected using shaky instruments.

The same assumption — that self-report alone is sufficient grounds for allowing an identity to be legally or clinically recognised — also played a role in the Dutch bill on self-identification that was introduced in 2021 and withdrawn again in 2024. While that bill concerned legal sex registration, this review concerns the clinical and research measurement of gender identity. In both cases, self-report is treated as a sufficient basis, even though the instruments intended to objectify that self-report do not themselves meet standard scientific criteria.

What this means in practice

For clinicians, researchers, and policymakers, the implication is clear: results collected with a non-validated instrument — and according to this review, that describes the majority of instruments in use — tell us less than is often suggested. A survey result about "how many young people are non-binary" or an intake score intended to establish gender dysphoria is only as reliable as the instrument used to obtain it. Until even ten instruments achieve a high-quality rating, any figure based on self-reported gender identity deserves a substantial caveat.

Sources

Ahmad N, Ruetas A, Shaikh U, Sant'Ana TT, Mollayeva T, "Systematic review of instruments for measuring sex and gender attributes: assessment of measurement properties and utility in research on clinical and functional outcomes", Biomedical Engineering OnLine, 6 mei 2026. pmc.ncbi.nlm.nih.gov/articles/PMC13317429