The last couple of messages have alluded to the issue of independent risk
factors and if the benefit of treating more than one risk factor is
additive.
To date, as far as I am aware, all the multiple risk factor intervention
trials have shown no clinical benefit - Systematic review of randomised
controlled trials of multiple risk factor interventions for preventing
coronary heart disease - BMJ 1997;314:1666 - 7 June
In addition, if you reduce your cholesterol the chance of CHD decreases by
30%; if you treat your hypertension you reduce your chance of CHD by 20% and
if you treat your diabetes you reduce it by 25% and if you stop smoking you
reduce your chance by 40%. These numbers add up to 115% which is impossible
unless you are able to decrease the chance of CHD in the person standing
next to you.
In this regard, I have a couple of questions for the group:
1) If one reduces so called independent risk factor why does that not
produce additive benefits?
2) In cohort studies where risk factors have been shown to be independent by
covariance analyses - does it mean that they should produce additive effects
when applied to patients with multiple risks. They appear not to, so why
not? Are they really completely independent or just different enough to
produce a statistical difference?
3) When covariance analyses are done on data from RCT's to show independent
effects does that mean that these interventions should produce additive
effects?
Any help to clarify these issues would be appreciated.
Dr James McCormack
Associate Professor
Faculty of Pharmaceutical Sciences
University of British Columbia
Vancouver, B.C.
604) 822-1710
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