"In two level factorial designs experiments are done at all possible level combinations. That is experiments, where k is the number of factors. There are always as many parameters as there are level combinations. The most useful parametrization is based on the ordinary ANOVA model. We have one constant term and the other parameters are main effects, two factor interactions and higher order interactions. When no replicates are done we will have no direct estimate of error, but we can often assume that higher order interactions are negligible."

http://www.matforsk.no/ola/thesis/