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2009 Jul 13
0
testing equality of two dependent correlations + normality issue
...coefficients in a setting with three variables X,Y,Z, i.e. equality of r(X,Y) and r(Z,Y). I have found a formula to transform the "2 dependent correlations difference" to t-distribution with N-3 df: t = (rxy - rzy)* SQRT[{(n - 3)(1 + rxz)}/ {2(1 - rxy^2 - rxz^2 - rzy^2 + 2rxy*rxz*rzy)}] (Blalock, H., 1972. Social Statistics. NY: McGraw-Hill. Page 406-7). Am actually not sure whether this is exact or approximate (even given normality assumption, the Fisher's Z-transform which this is - I assume - based on, is approximate, right?). But to make it a bit more complicated, Shapiro-Wilks tes...