Prevalence of a disease plays an important role in your probability of having it given you test https://abs.twimg.com/emoji/v2/... draggable="false" alt="➕" title="Heavy plus sign" aria-label="Emoji: Heavy plus sign">
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🙅‍♀️" title="Woman gesturing not ok" aria-label="Emoji: Woman gesturing not ok"> less relevant for testing COVID-19 infection since RT-PCR rarely (if ever) has false https://abs.twimg.com/emoji/v2/... draggable="false" alt="➕" title="Heavy plus sign" aria-label="Emoji: Heavy plus sign">
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🤷‍♀️" title="Woman shrugging" aria-label="Emoji: Woman shrugging"> may be relevant for antibody tests, which are less precise
https://youtu.be/I63OGstyQ3w ">https://youtu.be/I63OGstyQ...

The numbers I have here are all made up, the https://abs.twimg.com/emoji/v2/... draggable="false" alt="💡" title="Electric light bulb" aria-label="Emoji: Electric light bulb"> general idea is if your probability of having a disease is low, and a test is not *perfect*, your probability of having the disease given you test https://abs.twimg.com/emoji/v2/... draggable="false" alt="➕" title="Heavy plus sign" aria-label="Emoji: Heavy plus sign"> may be low

The methods used to test for current COVID-19 infection likely don’t suffer from false positives (although false negatives are possible and there are other potential issues that I highlight in this thread https://abs.twimg.com/emoji/v2/... draggable="false" alt="🧵" title="Thread" aria-label="Emoji: Thread"> https://twitter.com/lucystats/status/1248307278404554759?s=21)
https://twitter.com/lucystats... class="Emoji" style="height:16px;" src=" https://abs.twimg.com/emoji/v2/... draggable="false" alt="☝️" title="Up pointing index" aria-label="Emoji: Up pointing index"> But the antibody tests may be less precise

https://twitter.com/lucystats/status/1248307278404554759?s=21