```Date: Wed, 13 Aug 1997 19:37:33 GMT Reply-To: Richard F Ulrich Sender: "SPSSX(r) Discussion" From: Richard F Ulrich Organization: University of Pittsburgh Subject: Re: significance of correlation coefficient Richard Batt (rbatt@arts.adelaide.edu.au) wrote: : Hi! : For a simple correlation (N=35) SPSS 7 for Windows gives p = 0.05 for : approx r = 0.330. However when I check by hand using, : p_val = 1 - CDF.T(t,33) where t = r * sqrt( (33/(1-r^2) ) : I get p = 0.05 for approx 0.295. Any suggestions as to why the : discrepancy? In my simulations I was doing multiple correlations, : perhaps SPSS adjusts the p value for this? - If you are doing MULTIPLE CORRELATIONs then you are looking at multiple Rs which are inherently two-tailed. You have described your first correlation in contradictory ways, when you say "simple" and then "multiple". The CDF gives you one tail, which yields a one-tailed p-value, as you show above. Rich Ulrich, biostatistician wpilib+@pitt.edu http://www.pitt.edu/~wpilib/index.html Univ. of Pittsburgh ```

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