🌹🌷🌞🙏 *CHAPTER 19* THE DUBIOUS EFFICACY OF DOCTORS, CONSULTANTS AND PSYCHOTHERAPISTS.* *Regression to Mean* His back pain was sometimes better, sometimes worse. There were days when he felt he could move mountains, and those when he could barely move. When that happened, he would visit a Chiropractor. The next day you would feel much more mobile and recommend the therapist to everyone. Another man, younger and with respectable golf handicap of 12, gushed in similar' fashion about his instructor. Whenever he played miserably, he booked an hour with the pro, and lo and behold, in the next game he fared much better. A third man, and investment advisor at a major bank invented a sort of rain dance performed in the restroom every time his stock set performed extremely badly. As absurd as it seems, he felt compelled to do it and things always improve afterward. What links the three men is a fallacy: the *regression to mean* delusion. Suppose your region is experiencing a record period of cold weather. In probability, the temperature will rise in the next few days, back toward the monthly average. The same goes for extreme heat, drought or rain. Weather fluctuates around a mean, golf handicaps, stock market performance, luck in love, subjective happiness and test scores. In short, the crippling back pain would most likely have improved without a chiropractor. The handicapped would have return to 12 without additional lessons. And the performance of the investment advisor would have also shifted back toward the market average - with or without the rest room dance. Performances are interspersed with less extreme once. The most successful stock picks of past 3 years are hardly going to be the most successful stocks in the coming 3 years. Knowing this, you can appreciate why some athletes will rather not make it on to the front pages of the newspaper, subconsciously they know that the next time they race, they probably won't achieve the same top result - which has nothing to do with the media attention, but is to do with the natural variations in performance. Take the example of a division manager who wants to improve the employee morale by sending the least motivated 3% of the work force on a course. The result? Next time you looks at motivational level, the same people will not make up to the bottom few - there will be other. Was the course worth it? Hard to say, the group motivation levels would probably have returned to the personal norms even without the training. The situation is similar to the above 3 cases. Another example, in Boston, lower performance schools were entered into a complex support program. The following year, the schools had moved up in the rank, and improvement that authorities attributed to the program rather than to natural regression to mean. Sometimes, ignoring regression to mean can have destructive consequences too, such as Teachers (or Managers) concluding that the stick is better than the carrot. For example, following a test the highest performing students are praised, and the lowest are castigated. In the next exam, other students will probably - purely coincidentally - achieve the highest and lowest scores. Thus the teacher concludes that reproach helps and praise hinders. A fallacy that keeps on going. In conclusion: when you hear stories such as - the company had a bad year, so we hired consultant in and now the results are back to normal - *look out for our old friend - the regression to mean error*. *End of chapter 19* Book Extract 5 - The Art of Thinking Clearly - By Rolf Dobelli, Translated by Nicky Griffin, Published by Hodder & Stoughton Ltd., London, UK. Compiled by : Mahendra Kolhekar X Handle : @KolhekarM 🌹🌷🌞🙏