dennis roberts <[EMAIL PROTECTED]> wrote:
[regarding the "point biserial correlation"]
> and it certainly has nothing to do with a "shortcut" formula for
> calculating r ... it MAY have decades ago but .... it has not for the past
> 20 years ...
While I certainly agree that many textbooks convey the absolutely
misleading impression that the "PBC" is some special form of measure, I
think that the usual formula presented for it is pedagogically useful in a
few ways (not that the typical textbook makes use of them):
1) It demonstrates that a correlation problem in which one variable is
dichotomous is equivalent to a two-group mean-difference problem.
2) It shows that in such a case, the correlation coefficient is a function
of both a standard effect-size measure (Cohen's d) and the relative sizes
of the two groups.
2a) It demonstrates that variations in the relative sizes of the group
will result in variations in the magnitude of the correlation, even if the
effect size is held constant.
=================================================================
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
http://jse.stat.ncsu.edu/
=================================================================
