On the interval - ratio distinction, I draw some zinnias in colored chalk on the board and measure them on an equal-interval scale that has a zero point at the level of the bottom of the chalkboard. But then I reveal the secret that some zinnias do not "start" at the same zero point (they were sunk too deep into the ground). So the ratio (e.g. multiplication, division) statements we previously generated (e.g. zinnia A = 2* zinnia B) are not true. But, operations of addition and subtraction still hold (e.g. difference between Zinnia A and Zinnia B = difference between Zinnia C and Zinnia D). To be honest, I enjoy these discussion more than students do. I then quickly jump to more psychological examples scaling beauty and intelligence. Beauty works good because most people compare others in beauty, and even make ratio statements (person A = twice as beautful as person B). (Wasn't there a movie called '10' in which 10 referred to scaled beauty ? ? ? ).
BUT, I think psychologists get too hung up on this topic (aside from the categorical - numeric distinction discussed by other tipsters, which is critical). A quick scan of some introductory statistics books written by statisticans indicates they don't beat the drum too loud on this issue. Of course, numbers "don't know where they come from." To me it all depends on what you end up talking about at the end of your study. If you scale "beauty" for instance, do you talk about beauty, or, just numbers from your particular scale? Because the existence of "beauty" (outside of your particular scale) is irrefutable, I'd mind my "ps and qs" and not assume equal intervals and definitely not true zero. You collect data with your scale, but then cast your research findings in terms os the underlying construct of beauty. But in the case of intelligence it is harder to separate the scale from the underlying construct. When people say "show me intelligence" they often point to a particular intelligence test. -- --------------------------------------------------------------- John W. Kulig [EMAIL PROTECTED] Department of Psychology http://oz.plymouth.edu/~kulig Plymouth State College tel: (603) 535-2468 Plymouth NH USA 03264 fax: (603) 535-2412 --------------------------------------------------------------- "What a man often sees he does not wonder at, although he knows not why it happens; if something occurs which he has not seen before, he thinks it is a marvel" - Cicero. --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]
