What do you mean by 90% accurate? Do you mean for every 1/10 people analyzed, a result is wrong? That would be a lot of false positives.
If the 15-year risk for the population taking the test is 10%, an unbiased 10% error rate would mean:
81% true negatives, 9% false positives, 9% true positives, 1% true negatives.
> Even with a false positive, the changes you would make (lifestyle changes, brain stimulation, continuous monitoring) would only be beneficial
Not if prioritizing them crowded out things you could be doing to address a real risk that is deprioritized because of the false result.
And, also, of course, an error rate doesn't have to be unbiased. With the same population, a test with these results would also be 90% accurate:
90% true negatives, 10% false negatives.