Why intuition is a poor guide regarding testing
Intuitively, and in an emergency situation, we may think that a 70-80%
accuracy rate is far from perfect but may still be “good enough.” But
this is where common sense and intuition gets us – and the public –
into trouble. If we input these figures in the BMJ calculator, we obtain
a catastrophic 30 out of 31 false positives (Figure 2).
In other words, at a 1% pre-test probably (background prevalence), just
one out of 31 positive test results is a true positive. And, again, we
have zero false negatives, so the tests are not missing true positives
in this scenario.