Re: st: Power calculation for Beta/Odds Ratios in logistic regressionmodels

[Nico Hutter <Nico.Hutter@psychologie.uni-freiburg.de>]

Dear Neil,

your hint has been very useful and enriching! Thanks.

best wishes

Neil Shephard schrieb:
> On 8/15/07, Nico Hutter <Nico.Hutter@psychologie.uni-freiburg.de> wrote:
>   
> > Hi everyone,
> >
> > we would like to run a power calculation for beta-coefficients / odds
> > ratios in logistic regression models with covariates.
> > Is such a procedure implemented in SATA?
> >
> > Used command for the logistic regression model:
> > svy: logit depression age sex comorbidity, or
> >
> > Data stems from a national representative survey. Dependent variable is
> > depression. Comorbidity is dichotomised. Now, we are interested in the
> > "post hoc" power of the odds ratio of comorbidity.
> >
> > Can anybody give us some advice, please? Thanks in advance!
> >     
> Roger Newson has pointed to an appropriate solution, but I would
> question why you wish to do this?
>
> In my opinion "post hoc" power is a meaningless measurement that is
> completely useless in interpreting results, and a practice that needs
> to discouraged.
>
> You have already done your test (logistic regression) and got your
> results.  Knowing the 'power' your data had of detecting this size of
> effect (or more likely lack of) will tell you nothing more informative
> about the association.  Its like trying to tell someone who's just one
> the lottery that they shouldn't buy lottery tickets because the chance
> of winning is so low, they're not going to care as they've already got
> their answer.
>
> There are a few papers around that discuss this in greater detail (I'm
> sure there are more).
>
> Neil
>
> References
>
> Goodman SN, Berlin JA (1994) The Use of Predicted Confidence Intervals
> when Planning Experiments and the Misuse of Power When Interpreting
> Results. Annals of Internal Medicine 121.3:200-206
>
> Hoenig J.M., Heisey D.M. (2001) The Abuse of Power: The Pervasive
> Fallacy of Power Calculations for Data Analysis. The American
> Statistician  55:19-24
>
> Levine M, Ensom MH (2001) Post hoc power analysis: an idea whose time
> has passed? Pharmacotherapy 21.4:405-409
>
>   

--
Nico Hutter, Dipl. Psych.
Abt. f�r Rehabilitationspsychologie und Psychotherapie
Institut f�r Psychologie 
Universit�t Freiburg
D-79085 Freiburg
Tel: +49(0)761/203-9172
Fax: +49(0)761/203-3040
http://www.psychologie.uni-freiburg.de/Members/hutter

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