Cox, D. R. (1957). Note on grouping. Journal of the American Statistical Association, 52, 543–7.
Dalenius, T. (1950) The problem of optimum stratification. Skand. Aktuar., 33, 203–13.
Dalenius, T. and Gurney, M. (1951) The problem of optimum stratification II. Skand. Aktuar., 34, 133–48.
Flury, B. A. (1990) Principal points. Biometrika, 77, 33–41.
Flury, B. A. (1993) Estimation of principal points. Applied Statistics, 42, 139–51.
Press, W. H., Flannery, B. P., Teukolsky, S. A. and Vetterling, W. T. (1988) Numerical Recipes in C. Cambridge University Press.
Tarpey, T. (1992) Principal Points. Doctoral Dissertation, Department of Mathematics, Indiana University.
Zoppè, A. (1992) I Punti Principali di Distribuzioni Univariate. Doctoral Dissertation, Department of Statistics and Operations Research, University of Trento.