On Fri, 7 Apr 2000, Chris Mecklin wrote:
Among other things
>
> My point is that I want to show my class an example where they can see the
> pitfalls of making a decision based solely on a p-value. I don't want
My favorite, not contrived example, has to do with vocational advice and
gender. It is well known that in high school boys do better on
standardized measures of mathematics and girls do better on verbal
measures. This lead to the "obvious" conclusion that girls should avoid
anything mathy in their career choices while boys should avoid the
humanities.
But, it turns out that the effect sizes for these results are typically
around d=0.1 with individual studies maxing out at about 0.2. (I can't
lay my hands on my notes right now, but these convert to an R^2 that is
fairlly small. Somewhere below .05.)
The significant findings all have large sample sizes in common. Typically
1000+ students, so the results are all p < .01.
If you think about these results in terms of variance accounted for
individual variability NOT associated with gender clearly overwhelms any
gender effects by about 19:1. If you think about these in terms of
overlapping distributions the top 48-49% of the girls are scoring in
roughly the same range as the top 50% of the boys for math with a similar
gender reversed result for verbal skills.
In other words this real relation between gender and ability tests is an
extremely poor substitute for individual information. Many girls have the
ability to do well in mathy areas and many boys lack the ability.
Michael
> them going "Ok, the p-value is .04 in this problem, so I don't reject, no
> wait, I reject, I think, Ok, yeah I reject, so whatever the treatment is
> must be good."
>
> ___________________________________
> Christopher Mecklin
> Doctoral Student, Department of Applied Statistics
> University of Northern Colorado
> Greeley, CO 80631
> (970) 304-1352 or (970) 351-1684
>
>
>
>
>
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*******************************************************************
Michael M. Granaas
Associate Professor [EMAIL PROTECTED]
Department of Psychology
University of South Dakota Phone: (605) 677-5295
Vermillion, SD 57069 FAX: (605) 677-6604
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All views expressed are those of the author and do not necessarily
reflect those of the University of South Dakota, or the South
Dakota Board of Regents.
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This list is open to everyone. Occasionally, less thoughtful
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