[jorleif]

While the answer to the question is quite good, the rant at the end really considers any kind of skepticism towards medicine "mumbo-jumbo". The key point is the accuracy of the medical prediction from the measurements. If you indeed have a tumor of the kind Jobs had, then it is certain that you will have problems. However, if you have mild hypertension or high cholesterol, you might have a problem, or then you might not. Treatment itself can cause problems of similar magnitude, and therefore being skeptical can be well founded.