The designation n/c indicates that a non-negative value of SS for the three-way interaction AxBxC cannot be calculated. This can happen when the design is substantially unbalanced. For a 2x2x2 analysis, a balanced design is one in which all eight cells in the analysis have equal values of n. The design is unbalanced in the degree that the eight cell values of n are heterogeneous. This simple version of a three-way ANOVA is not recommended for data sets with an unbalanced design.