don ... no wonder students go bananas in statistics ... if we "sink" to
this level of discussion about a formula ... a formula that really has so
little utility ... how much time do we spend on the really important ones?
i would submit that for most intro courses ... where correlation is
discussed prior to significance testing and/or effect sizes ... the
comparison and points you are making here about the pb correlation FORMULA
... are totally irrelevant ...
now, maybe at the end of the course ... one could lay out the most popular
25 formulas for things ... and then show connections between some of them
... that MIGHT be nice
but WHEN correlation is discussed? to link that to a t test and/or effect
size? or, even to bring to bring the formula into the conversation ... what
is the rationale for doing so when the basic PPM formula handles all of this?
let's see
i want to talk about the pb formula ... so as to show how IT relates to the
two sample t test ... when i haven't even talked about the t test yet ...
and i don't need the pb formula in the first place ... to find the
correlation between two variables, one that happens to be dichotomous
as for your reference to glass and hopkins ... they say: "when one
dichotomous variable ... is correlated with one continuous variable, the
formula for the product-moment correlation coefficient CAN BE SIMPLIFIED
.... [caps for emphasis ... ] ..."
they don't say it HAS to be simplified nor do they say it should be
simplified ... and, we all know of course that this statement ... has no
practical meaning anymore and hasn't been so since the introduction of the
simple hand held calculator ...
in what way is the formula simplified? it has been changed ... altered ...
rearranged ... resubstituted for ... but, the normal context of using the
word "simplified" in THIS specific case has been historically given in the
form of ... it makes it easier to calculate ...
so, what it appears to me is that the rationale for showing the pb formula
nowadays boils down to linking it to the two sample t test ... which i
suggest is a no brainer when, the pb formula does not have to be introduced
in the first place
At 08:27 AM 10/22/00 -0400, Donald Burrill wrote:
>"This formula" is ambiguous. Maybe the n's don't appear explicitly in
>the particular formula you're looking at, Dennis, but they must be there
>implicitly, as Eric observed for a formula involving p's and q's. As
>Glass & Stanley (1970, pp 163-4) pointed out, there are several ways of
>simplifying the standard expression for the product-moment correlation
>coefficient when one of the variables is dichotomous. One of these
>simplifications (reproduced in Glass & Hopkins 1984, the 2nd edition)
>contains the factor
=================================================================
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
http://jse.stat.ncsu.edu/
=================================================================
