The 'goodness-of-fit' Chi-square is calculated where Observed and Expected
frequencies are compared for each of k categories. Expected frequencies can
be calculated in three ways: (1) from a mathematical distribution, (2) from a
simple ratio, or (3) from a contingency table. Degrees of freedom in the Chi-
square is dependent upon which method is used to calculate the expected
frequencies. In order to be compared to a Chi-square the expected frequencies
should not be too small, i.e. not more than 20% less than 5.