Selecting Statistics

Statistical Test

Tetrachoric r

Statistical Measure

Refer critical ratio for tetrachoric r to a table of the unit normal curve

Notes

This measure depends on a strict assumption of the normality of the continuous variables that have been dichotomized. Furthermore, the sampling error is large when dichotomies are extreme. Nunnally (1978, pages 135-137) advises against the use of these coefficients.

Tetrachoric: McNemar, Q. Psychological Statistics. Fourth edition. New York: Wiley 1969. p. 221; Nunnally, J. C. Psychometric Theory. Second edition. New York: McGraw-Hill, 1978. p. 136

Critical ratio: McNemar, Q. Psychological Statistics. Fourth edition. New York: Wiley 1969. p. 223