References/Notes/Attributions:
Source
Weisberg, S. (1985) Applied Linear Regression. 2nd edition. Wiley, pp. 144–5.
Selected from: Allison, T. and Cicchetti, D. V. (1976) Sleep in mammals: ecological and constitutional correlates. Science 194, 732–734.
References
Venables, W. N. and Ripley, B. D. (1999) Modern Applied Statistics with S-PLUS. Third Edition. Springer.