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Re: ONEBGG post# 831

Tuesday, 08/30/2005 3:10:26 PM

Tuesday, August 30, 2005 3:10:26 PM

Post# of 915
A reader of this Gallery sent me a very amusing story.
He took advantage of one of those online offers...a free credit report. He was delighted to learn that his credit rating was better than 100% of those who had received such a report...which obviously included himself. "Whoopee!!!, he exclaimed, my credit rating was better than MY OWN!!! It just doesn't get any better than that."

*Harley(I need your last name), thanks for this cute anecdote. This does hit on a point that I have been frequently asked about. Can a person's score in any distribution fall at the 100th percentile or more precisely can his score have a percentile rank of 100? If you subscribe to classical test theory, the answer is technically NO. Suppose that person A had a top score of 23 on a 25 item test with the remaining 49 other students scoring below 23. Then assuming the scores are continuous, person A's true score would be between the real limits of 22.5 and 23.5. The only way that person A's score would have a percentile rank of 100 would be if his true score was between 22.5 and 23. Since it is just as likely that his true score is between 23 and 23.5, we generally compromise and assume 1/2 of his score is between 22.5 and 23 and the other half is between 23 and 23.5 (a whacky assumption but more plausible if you had several scores of 23). Thus the percentile rank of person A would be (49 + (1/2 x 1))/50 = 49.5/50 = 99. Most modern authers subscribe to the above line of thinking but as we all know, statistics is heavily laden with many assumptions.


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