Time is not the only predictor in a dataset. IF someone is projecting a future response, it does not mean does not even mean that time is actually one of the predictor. This is no different than predicting differences within a spatial context. Space or time may or may not be a predictor, even though the response they are projecting occurs in the future or in a different place or both.
On Thu, Mar 6, 2014 at 12:20 PM, Soykan, Candan <[email protected]> wrote: > Mikaela, > Good for you to ask such a question! Most individuals don't even > think twice before extrapolating. The most notable examples that comes to > mind are the majority of climate change studies being done at present. > Predict far enough into the future and you are doubtlessly extrapolating > outside the bounds of your data. Does that mean that we shouldn't do it? I > would contend that extrapolation is acceptable under certain circumstances: > > 1) A prediction is better than none at all. Decisions will be made with or > without our scientific predictions. I would prefer that they be based on the > best available science. > 2) It is possible to extrapolate judiciously. Do your data follow a linear > trend? Is it ecologically reasonable for that trend to continue beyond the > bounds of your data? Consider a simplified example: Is it ok to assume that > a plant species response to temperature will follow a similar trajectory if > that temperature goes from 18 to 20 degrees C? Probably. On the other hand, > what if the temperature goes from -1 to 1 degrees C? Here an important > threshold (the freezing point of water) has been crossed, and we need to use > our biological, not statistical training to guide us. > > Having said that, if you do extrapolate beyond the range of your data, you > are introducing additional uncertainty into your results. Recognize and > address this uncertainty in your interpretation of the results. > > Good luck, > Candan Soykan > > > > -----Original Message----- > From: Ecological Society of America: grants, jobs, news > [mailto:[email protected]] On Behalf Of Mikaela Gioia Howie > Sent: Thursday, March 06, 2014 6:25 AM > To: [email protected] > Subject: [ECOLOG-L] Is it ever appropriate to extrapolate past your data? > > Hi Eco-loggers, > I was just wondering if anyone would like to weigh in on the issue of > extrapolation past one's data in order to make a prediction? Can this be > appropriate for a peer-reviewed publication? What other methods can be > employed to make simple predictions rather than extrapolation? Basically, I > am using regression models to predict what would happen at a point that is > outside of my dataset. I realize that this is would not be a robust > prediction but I have not determined another method to make a similar > prediction. > Thanks for your help! > Mikaela > > Mikaela G. Howie -- Malcolm L. McCallum Department of Environmental Studies University of Illinois at Springfield Managing Editor, Herpetological Conservation and Biology "Nothing is more priceless and worthy of preservation than the rich array of animal life with which our country has been blessed. It is a many-faceted treasure, of value to scholars, scientists, and nature lovers alike, and it forms a vital part of the heritage we all share as Americans." -President Richard Nixon upon signing the Endangered Species Act of 1973 into law. "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.
