Thanks.

This may imply some heuristics. Don't trust linear corelations in biology. Don't trust thresholds which are supposed to apply to everyone, or almost everyone. Be dubious about round numbers.

I agree blood pressure is a generally a poor predictor of health or mortality.

This is often measured because it is easy to measure, rather than it being particularly informative.

Aelephant - that's a good paper with data on this. I needed to edit that link to http://www.math.ucla.edu/~scp/publications/mortality.PDF for the pdf download to work.