I get where you're coming for (you want to draw conclusions for yourself, not for a whole population), but I don't think that is as you paint it.
You are not a good observer of yourself. You have biases and subjectivity when "measuring" yourself, so that makes your own "measurements" of yourself unreliable. Furthermore, there are certain observations you cannot even make. For obvious reasons, you cannot even do something so simple as estimating the effect on life expectancy :).
> You have biases and subjectivity when "measuring" yourself
As do the nurse who draws your blood, the tech who tests it, and the doctor who interprets the results. By all means recruit them to assist in your study, but don't do it in blind faith.
> that makes your own "measurements" of yourself unreliable
Perhaps in some ways and for some metrics, but conversely you are the best at knowing where you experience pain, how you "feel," and how today differs from yesterday.
> you cannot even do something so simple as estimating the effect on life expectancy :)
You are not a good observer of yourself. You have biases and subjectivity when "measuring" yourself, so that makes your own "measurements" of yourself unreliable. Furthermore, there are certain observations you cannot even make. For obvious reasons, you cannot even do something so simple as estimating the effect on life expectancy :).