How do they know how many undiagnosed?

danziger said:

I’m doing some research for a writing project that touches on my experience of T2 but don’t have a science background so don’t really get this.

When researchers say how many people have type 2 but don’t know it, what is that based on/how is it calculated/what is that extrapolated from?

TIA to anyone who can help!

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In my experience this sort of guesstimate is usually based on an extrapolation. For instance: someone looks at a number of people who have (eg) not been diagnosed with T2, and then tests their blood glucose. Suppose 100 are tested and 10 have glucose at "diabetic" levels. So 10% of undiagnosed people "have diabetes" and don't know it. So...10% of the country's undiagnosed population can be claimed to "have diabetes" and be unaware. There's a lot wrong with this sort of calculation - the initial test population is very small, it may not be typical of the wider population, etc. It's a huge jump to extrapolate from a small sample one-off to making statements about the population, but it's done all the time. The attached article is a good read on junk science. https://gizmodo.com/i-fooled-millions-into-thinking-chocolate-helps-weight-1707251800

Not just those types of studies!
Dodgy methodology or selective subject recruitment (biased towards sponsor's desired outcome) are rife. I think an ex-editor of the BMJ suggested well over 50 % of studies are actually biased garbage.

Oldvatr said:

I think the GP records and hospital records may be a source of data for the larger population.

Here is a paper on this topic
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3781536/

This is how UK,gov does it
https://assets.publishing.service.g...le/612306/Diabetesprevalencemodelbriefing.pdf

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The PHE (not UK gov, only England) paper referred to stresses "estimates" throughout. It is still guesswork based on assumptions - maybe much better assumptions but data are soft. Getting access to actual medical records even for the purposes of research is difficult (in some cases impossible) time consuming and expensive.

Edited to include a link to the relevant organization for England. https://www.hra.nhs.uk/approvals-amendments/what-approvals-do-i-need/confidentiality-advisory-group/