Dear all:

One of the easiest things to design is a negative study.  Just because there is no statistical 
significance, doesn't mean that there is no causality.  It can happen easily if the sample size 
is too small, measurement error is too great and all sorts of other forms of statistical bias.  
More frequently, it occurs because of issues of plausibility --- whereby the researchers 
didn't fully evaluate the mechanisms they intended to test.  

The link I sent was for an excellent study that review causality. ONLY ONE OF THE CRITERIA 
was experimental studies.  It gave beautiful cases for the case against tobacco within this 
larger framework.

Math is just simply not enough.

Best, Susan

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