```Date: Mon, 17 Jun 1996 11:37:11 -0500 Reply-To: abdu elnagheeb Sender: "SAS(r) Discussion" From: abdu elnagheeb Subject: logistic regression question for SAS To make it more clear, here is an example. Suppose you have 100 observations with your binary variable (say y) has 25 ones (good) and 75 zeros (bad). You want your predicted probability of good to be as close to one as possible (I assume you model Pr(good) here ; Pr(bad)=1-Pr(good) ) for y=1. Also Pr(good) for any y=1 should be greater than pr(good) for y=0 (i.e. all goods should have higher Pr(good) than do the bads.) What SAS does is: create all possible pairs of good and bads (here it is 75*25) . Then for each pair (of good and bad) compares the predicted Pr(good). If Pr(good) for the y=1 is greater than Pr(good) for y=0, this pair is "concordant". If it is the opposite it is "discordant", else it is a tie. Then you count the number of Concordant divide by 75*25 (all possible pairs) to get the proportion. Do the same for discordant and ties. I hope this will help. Abdu -------------------------------- ATTACHED NOTE -------------------------------- Date: June 17, 1996 From: S4BFF09F - MAILHUB1 To: Multiple recipients of l S4BFF0B0 - MAILHUB1 Subject: logistic regression question for SAS ------------------------------------------------------------------------------ Dear Readers, Can someone tell me the meaning of discordant and concordant in the PROC LOGISTIC procedure in SAS. How are they calculated? Also, does anyone have references for the correlation indices : Somer' D, Kendall's tau-a, Goodman-Kruskall gamma, and c. Does anyone have an explanation for the c table that is also generated in logistic procedure. thankyou, Paul Turner ```

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