CRAMER PHI MEASURE OF ASSOCIATION
http://www.psych.cornell.edu/Darlington/crosstab/table3.htm
The Cramer phi and phi2 are simple transformations of the familiar
Pearson chi-square statistic for testing association in a frequency table.
This statistic uses the familiar formula:
chi-square = SUM((o-e)^2/e)
where e = row total * column total / N
phi = sqrt(chisquare/(N(MRC-1)))
In 2x2 tables the Cramer phi reduces to the absolute value of the
familiar phi-coefficient, which in turn equals the Pearson correlation
between the row and column variables when both variables are coded
numerically such as 0-1 or 1-2.
Similarity [0, 1].
Usage: for binary data.