It is interesting that so many researchers bring up the issue of "correlation doesn't demonstrate causality" and yet are more than happy to argue causation based on regression, which usually relies on the same sort of data as used for standard correlational analyses.
Regression analyses are not typically used for experimental data and thus are asserting causation based on correlation. The practical difference between regression and correlation is the a priori hypothesizing of causation (how many regressions are really conducted post hoc after examining scatter plots is a whole other can of worms). The exact same statistical results in terms of "F's", "P's" and R^2 will be obtained if you switch which variables are dependent and independent in a linear analysis (of course intercepts and coefficients would differ). I mention this in relation to the below post because when discussing path analysis with a colleague awhile back the comment was made that "correlation=/=causation" to which my reply was "that's what you do with regression". Although path analysis does use correlation matrices (or covariance matrices) in its analysis I consider it to be more akin to multiple regression as you're testing a priori causal hypotheses. Next time someone asserts correlation doesn't demonstrate causation ask them when the last time was that they used regression. The ensuing argument can be quite amusing. Ned Dochtermann -- Ned Dochtermann Department of Biology University of Nevada, Reno 775-784-6781 [email protected] www.unr.nevada.edu/~dochterm/ -- Quoting William Silvert <[email protected]>: > Since I think that Mao Tse Tung and Pol Pot were heavy smokers, to say > nothing of Fidel Castro, I guess that where Malcolm is going is to show that > by selecting your data you can obtain any correlation you want. > > The point that correlation alone does not prove causality is one that > statisticians are always making, but mention should be made of Path > Analysis, a technique based on multiple correlation, that is effective in > establishing causal pathways. It is used extensively in the social sciences, > but only rarely in ecology. I think that it deserves more attention, I have > certainly found it of value. > > However a benthic ecologist I know who used Path Analysis died young, so > although that is only one data point, perhaps Path Analysis should be > avoided! > > Bill Silvert > > ----- Original Message ----- > From: "malcolm McCallum" <[email protected]> > To: <[email protected]> > Sent: sexta-feira, 4 de Dezembro de 2009 18:13 > Subject: [ECOLOG-L] an example of a false correlation > > > > Anyone who teaches stats might be interested in this false correlation I > > just stumbled on. > > > > 1) Stalin did not smoke > > 2) Hitler did not smoke > > 3) Mussolini (sp?) did not smoke. > > 4) Roosevelt smoked > > 5) Churchill smoked > > > > I guess you can see where I'm going with that! > > :) > > > > -- > > Malcolm L. McCallum >
