Hi One small change / addition to my earlier posting
James M. Clark Professor of Psychology 204-786-9757 204-774-4134 Fax [EMAIL PROTECTED] >>> "Jim Clark" <[EMAIL PROTECTED]> 01-Jun-08 1:28:26 AM >>> To illustrate, the third row selects cases above 700 (2 SDs above the mean), which amounts to about 16% of the 100,000 scores. The sample r of .4 produces a population rho of .70, quite close to the actual value. With extreme selection (bottom row, SAT > 800, .13% of scores), the formula appears to overcorrect. sdx r sigx sigx2 rho1 rho2 rho3 rho4 rho5 100.00 .7100 100.00 10000 .7100 .7100 .7100 .7100 .7100 59.000 .5200 100.00 10000 .7181 .7181 .7181 .7181 .7181 44.000 .4000 100.00 10000 .7042 .7042 .7042 .7042 .7042 33.000 .3100 100.00 10000 .7029 .7029 .7029 .7029 .7029 22.000 .2800 100.00 10000 .7984 .7984 .7984 .7984 .7984 JC: Rather than over-correction at SAT>800, estimate becomes more variable with extreme selection (or relatively small n), and I happened to report a high value. I ran the simulation 10 times with SAT>800 and obtained a mean correct r of .716 (close to expected value) but with SD corrected r = .131. Five simulations for SAT > 700 produced mean corrected r of .702 with SD corrected r = .023. Take care Jim --- To make changes to your subscription contact: Bill Southerly ([EMAIL PROTECTED])
