1. Whiting-O’Keefe QE, Henke C, Simborg DW. Choosing the correct unit of analysis in medical care experiments. Med Care. 1984;22:1101–14.
2. Kleinbaum DG, Kupper LL, Muller KE. Applied regression analysis and other multivariable methods, 2nd ed. Boston: PWS Kent, 1988.
3. Remington RD, Schork MA. Statistics with applications to the biological and health sciences, 2nd ed. Englewood Cliffs, NJ: Prentice-Hall, 1985.
4. Garfield E, (ed.). SCI journal citation reports. Philadelphia: Institute for Scientific Information, 1988;19:3–42.
5. Snedecor GW, Cochran WG. Statistical methods, 7th ed. Ames, IA: Iowa State University Press, 1980.