NNT

You may wonder why I said a healthy diet does not reduce the number of people with chronic medical diseases.

Let me give you a quiz on statistics:

For convenience, let’s take acute heart attack. Suppose the mortality is now 20%, and a new treatment would reduce the mortality to 10%. How many people do you have to treat so that one could get some benefit ?

“The number-needed-to-treat is 10.” I could hear you say.

Wrong. (That’s how most of us are fooled by thick-head statisticians.)

Look. We need to treat 10 to prevent one death, but the number of people who would get the benefit is much bigger.

Don’t you see the point? Here. One in ten patient should have died without treatment and now survived – with a class IV heart failure. Another patient in that ten who should have class IV heart failure without treatment now have class III, and so forth and so forth. If you are an administrator and just look at the numbers, for any ten patients, there’s one fewer death, and one more entirely healthy person – but actually the distribution curve of the cardiac status of the whole population shifted, and it is not the one who ought to die becomes completely well.

The point is: The total number of patient with some heart failure within that population remained the same. From the society point of view, it does not save any money – except that for a funeral. (I shall omit the social cost should the survivor is an elderly person.)

The same argument holds for your good old healthy diet.