Dear All,
I read a paper yesterday in which the amount of confounding
occurring was assessed by examining percentage change in Odds
Ratios between the exposure variable and the outcome
when each confounder was added.
Sentences like, "confounder X accounted for 32% of the size
of effect" were then used.
I am rather wary of this method - what happens when the OR
increases once a confounder has been controlled for? or worse,
what if a confounder reverses the direction of the effect?
150% of effect accounted for? or some such rubbish.
Having said this, In my current problem, I have a three-level
exposure variable so this method would be quite useful in
assessing the effect of confounding on the difference between
those three levels - e.g. this variable reduces the difference
between levels 1 and 2, but does not affect the difference
between 1 and 3 - something I don't think I could do purely by
looking at the likelihood.
So my question is - is this a valid method or not?
Any thoughts/references would be gratefully recieved.
thanks
Jon
============================
Dr Jon Heron
University of Bristol
============================
|