Introducing the concept of a "design matrix", this paper relates the regression analysis, the analysis of variance, and the analysis of frequency counts to the use of the least squares method. It is demonstrated with some simplifiedexamplesshowing that,givenaproperlyarrangeddesignmatrix, the analyses of means, probabilities, and frequencies share the same least squares approach as that of the regression analysis. Special attention is called to the "orthogonal" design matrix which results in independent parameter estimations jointly. Researchers are urged to review the possible arrangements of the design matrix before actually doing on the estimation.