61. Analogous to a Latin square, a Greco–Latin square design can be used when it is suspected that three extraneous factors may affect the response variable and all four factors

(the three extraneous ones and the one of interest) have the same number of levels. In a Latin square, each level of the factor of interest (C) appears once in each row (with each level of A) and once in each column (with each level of B).