General Linear Model for a Latin Square:
In design of experiment, a Latin square is a three-factor experiment in which for each pair of factors in any combination of factor values occurs only once.
Consider the following Latin Square,
where rows correspond to 4 values of factor I, columns - to 4 values of factor II, and letters to 4 values of factor III.
A general linear model for this experiment is
where Yijk are observed values of the dependent variable, 
are effects corresponding to the 4 values of factor I, 
- of factor II, 
- of factor III, eijk are random variations.
Note: the Latin square is appropriate only if effects of all three factors are additive - that is, all interaction effects are zero.