The whole point of a correlation is that you don't really know what is going one with two or more variables, but you think there might be a relationship of some kind. That is why we say correlation doesn't indicate causation. A regression does indicate causation because we name a determinant variable. For example, if you take a bunch of guppies in a glass of water and add salt until the die, then you are testing to see how much salt kills guppies. You do a regression. However, if you go out in the wilderness and measure salt concentrations and count guppies for unrelated reasons, and after looking at your data you say, hey it looks like guppies might be getting killed by salt, you still do a regression because you are looking for the effect of salt on guppies, it sure isn't very logical even if narrowly possible that guppies are changing the salt concentration of the water. Now, if you are doing measurements on all kinds of data. YOu happen to notice that a lot of guppies are in ponds that also have plants. You have no idea if the plants are helping the guppies, if the guppies are helping the plants, or if some third factor is influencing both of their apperaance. SO, you run a correlation to see if the association you seem to observe is actually happening. Later, you can set up experimetns to determine why plants and guppies have correlated presence absence rates. In those following experiments you might use a regression. (this all assumes you have the experiment set up properly for the tests I mention!!!! :)
Make sense? On Tue, Oct 9, 2012 at 12:56 PM, Wayne Tyson <[email protected]> wrote: > Hi y'all, > > If I remember the quote correctly, it said "Correlation is not causation." > It did not say that it didn't imply causation. The distinction is crucial, > eh? (It appears that my initial response to the initial question didn't make > its way to Ecolog, possibly because I neglected to approve it or because it > was rejected. > > WT > > PS: Correlation is not in opposition to (v.) causation. > > Let us not jump to contusions. > > ----- Original Message ----- From: "Devan McGranahan" > <[email protected]> > To: <[email protected]> > Sent: Tuesday, October 09, 2012 8:57 AM > > Subject: Re: [ECOLOG-L] correlation v. causation > > >> Hi Shelley, others, >> >> Slate recently had a great article on correlation and causation with a >> historical perspective. >> >> My favorite line: "'No, correlation does not imply causation, but it >> sure as hell provides a hint." >> >> >> http://www.slate.com/articles/health_and_science/science/2012/10/correlation_does_not_imply_causation_how_the_internet_fell_in_love_with_a_stats_class_clich_.html >> >> >> >> >> >> >> >> "Having nothing better to do, I set fire to the prairie." >> -- Francis Chadron, 1839, Fort Clark, North Dakota >> >> http://www.devanmcgranahan.info >> >> >> ----- >> No virus found in this message. >> Checked by AVG - www.avg.com >> Version: 10.0.1427 / Virus Database: 2441/5317 - Release Date: 10/08/12 >> > -- Malcolm L. McCallum Department of Molecular Biology and Biochemistry School of Biological Sciences University of Missouri at Kansas City Managing Editor, Herpetological Conservation and Biology "Peer pressure is designed to contain anyone with a sense of drive" - Allan Nation 1880's: "There's lots of good fish in the sea" W.S. Gilbert 1990's: Many fish stocks depleted due to overfishing, habitat loss, and pollution. 2000: Marine reserves, ecosystem restoration, and pollution reduction MAY help restore populations. 2022: Soylent Green is People! The Seven Blunders of the World (Mohandas Gandhi) Wealth w/o work Pleasure w/o conscience Knowledge w/o character Commerce w/o morality Science w/o humanity Worship w/o sacrifice Politics w/o principle Confidentiality Notice: This e-mail message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message.
