1/ A test helps to determine whether you have a feature or not.

Good tests are precise: they predict a feature well, have high sensitivity/specificity, & low false positives/negatives.
2/ Precise biological tests do not exist for the most common mental disorders. There are some weak biological correlates for depression, but a weak correlate is not a test, the same way that a weak correlate of COVID (coughing) is not a test for COVID.
3/ How does this depression blood test do in terms of predictive accuracy?

The abstract of the paper has 773 (sic) words, 0 of which are about precision. No information on predictive accuracy, sensitivity/specificity, false positives/negatives, etc.

That& #39;s not good.
4/ Good tests have a second feature: they are specific to what we want to test. A COVID test should specifically test for COVID, not for the flu or for cancer.

I describe these 2 features of good tests (and some others) here: https://eiko-fried.com/all-mental-disorders-are-brain-disorders-not/">https://eiko-fried.com/all-menta...
5/ Overall, any paper about a blood test for depression requires evidence that the test correctly identifies depressed vs control cases (or, dimensionally, depression severity); and that it does *not* do so for e.g. anxiety or schizophrenia (otherwise it& #39;s not a depression test).
6/ Remember that the gold standard that blood tests are validated against is depression *as operationalized through a clinician& #39;s opinion*.

This is different from e.g. measles where we can know the true state of things to validate tests against (we cannot for depression).
7/ Simplified, if you have a really strong correlation of a test with the true state of measles (and not with that of the flu etc), then you have a good test.

This isn& #39;t possible, mathematically, for depression, because people disagree on the true state of depression.
8/ Agreement on the true state of depression (inter-rater reliability) was 0.28 in DSM-5 field trials. That is much, much, much lower than for many medical disorders, and about half of that of e.g. borderline personality disorder.
9/ Let me know you how 0.28 looks like.

On the left side is the true state for 100 people: 1/orange is depressed, 0/green is healthy.

On the right side, 2 clinicians see these patients, with an inter-rater reliability of 0.28.

Red fields = disagreements.
10/ So not only does this paper not provide a precise and specific test for depression; in my view, it *cannot* do that because the criterion is not clear.

This is why the author& #39;s goal to help psychiatry "become like other contemporary fields such as oncology" is odd to me.
11/ And while the authors mention their company in the paper& #39;s COI, it is worth stating that they may try to sell these tests (I have no principled concerns about this, but seems worth pointing out for transparency reasons given that it& #39;s not mentioned in the uni press release)
12/ I& #39;ll conclude with some more reading in case you are interested in the above.

First, here is a thread about depression heterogeneity, with a bunch of papers. This heterogeneity greatly limits the possibilities of blood tests and markers. https://twitter.com/EikoFried/status/935098850439847937">https://twitter.com/EikoFried...
15/15 Overall, the authors did tons of amazing & very sophisticated work, over many years, & deserve our praise. The field would be much poorer without them & their contributions.

But they have not developed a reliable & precise blood test for depression.
You can follow @EikoFried.
Tip: mention @twtextapp on a Twitter thread with the keyword “unroll” to get a link to it.

Latest Threads Unrolled: