Re:Cheap blood test detects pancreatic cancer before it spreads
by mlyle on Thursday February 13, 2025 @10:43PM
(#43044600)
Yah, I'm well familiar with the base rate fallacy and I still catch myself screwing it up. It's so unintuitive. I use mental math a lot to counter my intuition.
If sensitivity is high and the base rate is low, you can approximate it with .01 / (1-.91).
Or, mental math assuming 10,000 people is not unreasonable for your case (100 with disease, 90 true positives; 9900 * 9/100 false positives.. divide everything by 9 to make it easier, 10 true positives and 99 false positives, or 10/109 or say "9%".
If sensitivity is high and the base rate is low, you can approximate it with .01 / (1-.91).
Or, mental math assuming 10,000 people is not unreasonable for your case (100 with disease, 90 true positives; 9900 * 9/100 false positives.. divide everything by 9 to make it easier, 10 true positives and 99 false positives, or 10/109 or say "9%".