Calculates the analysis of variance when there are two factors that may
affect the dependent variable. Because the input is represented as an array, we
can refer to these two factors as the row-effect and the column effect. Unlike
the one-way ANOVA, there are mathematical difficulties with the two-way ANOVA if
there are unequal cell sizes; therefore, we require all cells to be the same
size, and so the input is a three-dimensional array.

The result of the analysis is an anova-table, as described in the manual. This
function differs from `anova-two-way-variables' only in its input
representation. See the manual for further discussion of analysis of variance.