I like the way this New York Times article explains that there is such a thing as too much screening. A nugget:
Much of our discomfort with the panel’s findings stems from a basic intuition: since earlier and more frequent screening increases the likelihood of detecting a possibly fatal cancer, it is always desirable. But is this really so? Consider the technique mathematicians call a reductio ad absurdum, taking a statement to an extreme in order to refute it. Applying it to the contention that more screening is always better leads us to note that if screening catches the breast cancers of some asymptomatic women in their 40s, then it would also catch those of some asymptomatic women in their 30s. But why stop there? Why not monthly mammograms beginning at age 15?
Stick with him through the math, because he makes a good point. Basically, false positives can have a big effect on whether or not a screening program really works. I also like how he talks about survival measurements:
Another concern is measurement. Since we calculate the length of survival from the time of diagnosis, ever more sensitive screening starts the clock ticking sooner. As a result, survival times can appear to be longer even if the earlier diagnosis has no real effect on survival.
So… we need to consider some pretty nerdtastic factors when we’re talking about screening, including probabilities, sensitivity, specificity, and measurement. I GD love epidemiology!