4 ms·
There was a seminar given to the breast cancer society by an epidemiologist years who who presented them with a scenario: Prevalence of breast cancer: 1% Sens
by dillydogg 2y ago
There was a seminar given to the breast cancer society by an epidemiologist years who who presented them with a scenario:
Prevalence of breast cancer: 1%
Sensitivity (percent of people who have the disease test positive): 90%
Specificity (percent of people without the disease test negative): 91%
And asked, "How many people who test positive have the disease?" (i.e., positive predictive value)
It's only 1/11. I think only 20% got it right (in a 4 answer multiple choice question)
- mlyle 2y agoYah, 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%".