You&#x27;re right. You have to update the probability with all the knowledge you have. Although I would say self diagnosis has a very, very high false positive rate, and if you know you&#x27;re a hypochondriac that would make the probability drop, plus we don&#x27;t even have a test for this that is 90% accurate. I&#x27;m not sure the difference is an order of magnitude :)<p>I think my point stands that it doesn&#x27;t make sense to test for extremely rare diseases because of a self diagnosis.