On 2 Dec 2002 at 19:03, Hugh Foley wrote: > Your biggest problem is that you used a 4-pt > scale. Had you kept the same structure as the original scale, I think > that a comparison would have been reasonable. To me, the issue goes > beyond the simple assignment of numbers to the scale points (which > could be open to challenge, even though everyone does so). With 4 > points, a respondent cannot choose a mid-point, but is forced to one > side or the other. With 5 points, a respondent can choose a neutral > response. Thus, I cannot think of a way I could re-scale your data that > would allow me to treat the two studies as comparable.
Well, when logic and thought fail to solve the problem, it's time for an experiment. Suppose (this being a thought experiment) someone asked subjects to rate various and sundry qualities, only some got to rate using a four-point scale, and others a five. Then one could examine the data to see what transformations, if any, could bring the means and SDs of the two scales into correspondence. Of course, the answer could be none. And, of course, if you're going to go to all the trouble of doing the experiment, it might be easier just to re-do the original with a 5-point scale. The answer to that one is to turn the problem into the deeper one of the general case: what transformation will turn a mean derived from a scale of x points into a mean from a scale of y points? If I'm following Hugh correctly, he'd predict that means from odd-numbered scales could be adjusted to fit means from other odd-numbered scales, and ditto for even-numbered scales. But you wouldn't be able to turn a mean from an odd scale into a mean from an even scale. Has no one ever looked into this problem? Stephen _______________________________________________________ Stephen L. Black, Ph.D. tel: (819) 822-9600 ext 2470 Department of Psychology fax: (819) 822-9661 Bishop's University e-mail: [EMAIL PROTECTED] Lennoxville, QC J1M 1Z7 Canada Department web page at http://www.ubishops.ca/ccc/div/soc/psy Check out TIPS listserv for teachers of psychology at: http://www.frostburg.edu/dept/psyc/southerly/tips ________________________________________________________ --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]
