Marie said: Now what doesn't make sense to me that two groups individually have positive and significant correlations but the two groups combined can have a negative and significant correlation. Here is an example I used when teaching Methods to students in a Criminal Justice program. Imagine two groups: psychology students and police officers. In both groups, you measure knowledge of psychology and skill at interrogating suspects. It is quite reasonable that, within each group, those who know more psychology will be better at interrogating suspects, so within each group these two variables have a positive relationship. However, when looking overall, we see one cluster high in psych knowledge and low in interrogation skills, and another cluster low in psych knowledge and high in interrogation skills, so the group as a whole shows a negative correlation.
Celia * * * * * * * * * * * * * * * * * * * * Celia Reaves, Ph.D. Department of Psychology Monroe Community College 1000 East Henrietta Road Rochester, NY 14623 Phone: 585-292-3258 email: [email protected]<mailto:[email protected]> From: Helweg-Larsen, Marie [mailto:[email protected]] Sent: Monday, February 27, 2012 12:08 PM To: Teaching in the Psychological Sciences (TIPS) Subject: RE:[tips] Statistical question-correlations --- 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=16300 or send a blank email to leave-16300-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
