Dear Mr Doherty (I apologise if the title is incorrect),
Your eyeballing is indeed accurate, and as you say it may be that we
get things wrong or get confused because we're told that screening
calculations are harder than they seem.
But sometimes, the numbers are a little less straightforward than in
the example given (prevalence 1%, sensititivity and specificity both
basically 90%), which is why I'd argue that it's probably better to learn
the important numbers to tell the patient (or, of course, if you don't
know, tell them you'll look it up and tell them later).
Competing interests: No competing interests