I'm curious to know why you're using the same exact exposure in different units. I've included a dichotomized version of a continuous exposure variable to look at potential threshold effects, but I've never heard of anyone doing what you've described.
At 08:28 AM 2/5/02 -0800, Wuzzy wrote: >Is it possible that multicollinearity can force a correlation that >does not exist? > >I have a very large sample of n=5,000 >and have found that > >disease= exposure + exposure + exposure + exposure R^2=0.45 > >where all 4 exposures are the exact same exposure in different units >like ug/dL or mg/dL or molar units. > >Nonetheless when I do a simple correlation (pearson) I found that the >exposure in ug/dL did not affect the disease. > >This seems hard to believe as my sample is relatively large.. >I don't believe the 0.45 R^2 is possible but was shocked by it. I'll >try to rerun it in other, more realistic models. > > >================================================================= >Instructions for joining and leaving this list, remarks about the >problem of INAPPROPRIATE MESSAGES, and archives are available at > http://jse.stat.ncsu.edu/ >================================================================= ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at http://jse.stat.ncsu.edu/ =================================================================
