Of course, the IQ score had a history of scoring that determined how the standardized IQ based on z-score would be calculated for the sake of consistency. When they converted from scores that were the result of dividing the Mental Age by the Chronological Age and multiplying by 100, it was desirable to continue to use 100 as the average score. Whereas it used to mean a Mental Age that matched the Chronological Age, it came to mean a score on the test that matched the average score for those in that age group. In any case, a raw z-score would be undesirable both for the fact that half of the population would have a negative IQ and the fact that an IQ of 2.00 or even 2.74 doesn't seem very impressive. Multiplying by 15 or 16 (which probably gave IQs somewhat equivalent to the old MA/CA x 100 system) and adding 100 to it, solved both problems.
Rick Dr. Rick Froman, Chair Division of Humanities and Social Sciences Professor of Psychology Box 3519 John Brown University 2000 W. University Siloam Springs, AR 72761 [email protected] (479) 524-7295 http://bit.ly/DrFroman "The LORD detests both Type I and Type II errors." Proverbs 17:15 -----Original Message----- From: Mike Wiliams [mailto:[email protected]] Sent: Sunday, September 30, 2012 2:09 PM To: Teaching in the Psychological Sciences (TIPS) Subject: Re:[tips] Is p < .05 ? Hello This is presumably why we have invented standard scores expressed as whole integers, such as IQ, SAT, T-score and GRE rather than use the original Z score. It is much easier to conceptualize an IQ score of 117 rather than an IQ of 1.13. I once designed a clipboard with an imprint that included a conversion table. Since Z is never used, it only included IQ, T and %tiles: http://brainmetric.com/clipboard4a.pdf You might find it handy as a tool illustrating the relationship of statistics to clinical testing practice. Mike Williams >> I hate to say this, but thank you. >> >> I have often wondered why so many students would be baffled by the >> decision process. [if p<.05, reject the null hypothesis]. It seems so >> easy... but, if you are not comfortable with the numbers between 0.00 >> and 1.00, then it is a real problem. >> >> --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13039.37a56d458b5e856d05bcfb3322db5f8a&n=T&l=tips&o=20813 or send a blank email to leave-20813-13039.37a56d458b5e856d05bcfb3322db5...@fsulist.frostburg.edu --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13090.68da6e6e5325aa33287ff385b70df5d5&n=T&l=tips&o=20828 or send a blank email to leave-20828-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
