Saturday, December 20, 2008

Chapter 2, Exercise 5, pg 45,49, 54,55 (correlation continued)

Posted on the companion web page is exercise 5, which covers how to obtain confidence intervals, and tests of significance for the basic bivariate correlation, the Spearman rank order correlation, the point biserial correlation, and the phi coefficient using the cor.test function in the R statistical computing program.

This covers pages 45 and 49 in the book and expands the exposition past basic bivariate correlation.

The second part of this exercise covers polychoric and polyserial correlation which is described on page 54 and 55 in the text. Specifically the book covers biserial correlation (not to be confused with point biserial correlation) and tetrachoric correlation. Both of these correlations concern variables (either one or two) that are artificially dichotomous. An example of an artificially dichotomous variable could be a variable that concerns a population that is best described on a continuum, yet is categorical in a data set (e.g. depressed, not depressed). The R package called polycor is used for these coefficients.

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