https:\/\/slate.com\/technology\/2022\/01\/rapid-testing-covid-math-false-negatives-sensitivity.html<\/a><\/p>\n\n\n\n

<\/p>\n\n\n\n

But they cut my draft down dramatically. I wanted to add a discussion of what is called “positive predictive value” (PPV) i.e. the answer to the question “if you test positive, do you have the disease?”<\/p>\n\n\n\n

If a disease is relatively rare (alas not Omicron) even a positive result with a very specific test can be very misleading and unfortunately can confuse your doctor (https:\/\/www.nejm.org\/doi\/pdf\/10.1056\/NEJM197811022991808<\/a>). <\/p>\n\n\n\n

Here’s an example of what can go wrong. Suppose you have a test that is 99% specific.\u00a0 If you read my Slate article you now know this means it only has 1% false positives. That is a pretty good test in the real world. But suppose the disease is also really rare, say only 1 in 1,000 people have it. Then it turns out that a positive test, even though the test is pretty darn good, isn’t telling you as much as you think! Why? Well, suppose you test 1,000 people.\u00a0Since we are assuming the disease prevalence is only 1 in a 1000, you had only one person with the disease in your group of a 1,000. Now our test is 99% specific so there are 1% false positives. So among our\u00a01,000 people, you will have about 10 false positives (.01*1000=10 although technically it is .01*9,999 =9.99). The 10 false positives dwarf the 1 true positive and the odds of you not<\/em><\/strong> having the disease are 10 to 1<\/p>\n\n\n\n

(A clear treatment of PPV in the context of Covid here: https:\/\/www.someweekendreading.blog\/weekend-editrix-exposed\/<\/a>)<\/p>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

https:\/\/slate.com\/technology\/2022\/01\/rapid-testing-covid-math-false-negatives-sensitivity.html But they cut my draft down dramatically. I wanted to add a discussion of what is called “positive predictive value” (PPV) i.e. the answer to the question “if you test positive, do you have the disease?” If a disease is relatively rare (alas not Omicron) even a positive result with a very specific test … Continue reading “Another slate article on Sensitivity and Specificity”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-694","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/posts\/694","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/comments?post=694"}],"version-history":[{"count":3,"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/posts\/694\/revisions"}],"predecessor-version":[{"id":697,"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/posts\/694\/revisions\/697"}],"wp:attachment":[{"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/media?parent=694"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/categories?post=694"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/garycornell.com\/wp-json\/wp\/v2\/tags?post=694"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}