Page 63 contains a footnote where I give the formula for the phi coefficient. Unfortunately, the denominator mixes up products and sums, so is incorrect. The correct formula should be:
phi = ad - bc / SQRT [(a + b) x (c + d) x (a + c) x (b + d)]
I'm grateful to John van den Bercken for pointing this out.
David
Saturday, 17 October 2009
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