I see them as different, too, Rick. With cyclical phenomena, _post hoc ergo propter hoc_ comes to mind, too.
m ------- Marc L Carter, PhD Associate Professor and Chair Department of Psychology Baker University College of Arts & Sciences ------- > -----Original Message----- > From: Rick Froman [mailto:[email protected]] > Sent: Monday, February 09, 2009 11:48 AM > To: Teaching in the Psychological Sciences (TIPS) > Subject: RE:[tips] [tips]Regression to the mean (was Bogus treatments) > > Others may differ, but I teach regression to the mean as > being a different phenomenon than what you might refer to as > capitalizing on the cyclical nature of an event. For example, > many people may not go to the doctor until their cold or flu > is at its worst which means that, by the time they get a > prescription, it is impossible to distinguish the effect of > the drug from the natural cycle of the illness. > > I explain regression to the mean as being due to the inherent > error in any test based on X = T + e (or the score on a test > (X) is the sum of the true score (T) plus or minus error (e)). > > This means that some extreme high scores are based on the > true score plus error. In those cases, the obtained score > will regress to the mean on second testing because > traditional testing theory assumes that the error is as > likely to decrease as to increase a score. Therefore, if you > choose the extremely high scores, the score on second testing > is likely to regress toward the mean (be lower) because the > error is unlikely to make such a positive contribution on > second testing. > > At the other extreme, some extreme low scores are based on > the true score minus error. In those cases, the obtained > score will regress to the mean on second testing (get higher) > because the error pulling the score down is not likely to be > as strong on second testing. So, if you sample just the > extremely low scores, the score on second testing is likely > to regress toward the mean (be higher) because the error is > unlikely to make such a negative contribution to the total > score on second testing. > > Do others make this distinction when discussing these effects? > > Rick > > Dr. Rick Froman, Chair > Division of Humanities and Social Sciences Box 3055 > x7295 > [email protected] > http://tinyurl.com/DrFroman > > Proverbs 14:15 "A simple man believes anything, but a prudent > man gives thought to his steps." > > > -----Original Message----- > From: Frantz, Sue [mailto:[email protected]] > Sent: Monday, February 09, 2009 11:15 AM > To: Teaching in the Psychological Sciences (TIPS) > Subject: RE: [tips] Bogus treatments > > > For regression to the mean, how about vitamin C to cure > colds? > (http://www.mayoclinic.com/health/cold-remedies/ID00036) > Everyone starts out with a cold, a day or two into it they > start drinking lots of orange juice, and a few days later > they feel better... which likely would have been the case > anyway, but they credit the orange juice. > > > --- > To make changes to your subscription contact: > > Bill Southerly ([email protected]) > --- To make changes to your subscription contact: Bill Southerly ([email protected])
