RE: correcting for chance

[Peterson, Douglas]

Not knowing exactly what judgment the participants made but assuming that the 2 choice experiment was (recent vs. non-recent) and the three choice was (recent, something in the middle or don't know, and non-recent) you could use variations on Signal Detection Theory - the computation for the 2 choice experiment is easier, but there are 3 choice SDT models.  You could then compare sensitivity of the two groups.   Just a thought and quite possible not appropriate - any others thoughts on this?   Doug   Doug Peterson Associate Professor of Psychology The University of South Dakota Vermillion SD 57069 (605) 677-5295 [EMAIL PROTECTED]   -----Original Message----- From: Steven Specht [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 24, 2004 10:13 AM To: Teaching in the Psychological Sciences Subject: Re: correcting for chance   If each of the group scores were converted to z-scores, wouldn't the z-score mean for each group (by definition) be equal to zero? So you would end-up comparing two zero scores (with a standard deviation of 1.00 for each group). Does your student want to know whether participants performed similarly on each test? If that's the case, might a correlation be performed across the two tests (then absolute scores and chance levels would not matter). "Manza, Louis" wrote: Patrick: A student has conducted 2 memory experiments and she would like to compare performance across the two (at least roughly).    The problem is that 1 of them was a 2-alternative forced choice test  and the other is 3-alternative forced choice test (both were judgments of relative recency).  Chance performance being substantially different between the two, a direct comparison isn't appropriate. Does anybody have a suggestion to correct for chance?  I thought of simply subtracting chance from each subject's score but I didn't know if that is acceptable or if there is a better idea. How about converting the raw scores into z-scores, and then comparing the z-scores across the 2 studies? Cheers, Lou ----------------------------------------------------------------------- Dr. Lou Manza  Associate Professor of Psychology  Lebanon Valley College  Annville, PA 17003  Phone: (717) 867-6193 Fax: (717) 867-6075  E-Mail: [EMAIL PROTECTED] "Living in the limelight, the universal dream, for those who wish to seem.  Those who wish to be must put aside the alienation, get on with the fascination, the real relation, the underlying theme." RUSH, "Limelight" ----------------------------------------------------------------------- --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED] -- |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| Steven M. Specht, Ph.D. Associate Professor of Psychology Department of Psychology Utica College Utica, NY 13502 (315) 792-3171 "unanswered questions are less dangerous than unquestioned answers"   --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED] --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]