How would you go about adjusting for that in an analysis?
I agree that it would be immensely useful to have such data but I can't think of anywhere where it exists or where such a degree of data linkage would be permitted. (I'd be very pleased if someone knows if data like this are available.)
The authors stated this as a plausible limitation:
More recent cohorts, particularly adolescents, may differ from those in earlier decades, and stress related to gender identity itself may be lower presently because of decreasing prejudice.
I agree that it's always difficult to compare and contrast across populations and healthcare systems. This publication is a standalone assessment of Finland. Because the evidence base is scant for CYP in this fraught area, the findings are a helpful contribution.
It will be a different analysis but useful in its own right when the York analysis of the GIDS data is completed and published. (Although it's increasingly likely that this will not be within the remaining lifespan of the Cass Review.)
NB: I'm delighted to see the March conference in London is sold out for in-person attendees (there is a waiting list). The livestream is free. I'm a little confused about the separate availability of livestream tickets but I think that's to streamline donations from those of us watching the livestream and it's not compulsory.