[R] Sample size

[Frank E Harrell Jr]

SAULEAU Erik-André wrote:
> Dear R-list,
> 
> I have to design the validation of a score (ordinal values between 0 and 6) reputed to separate 4 groups of patients with known frequencies in the population. I think the more accurate is to calculate sample size under median test. Is there a function for that in R (not in the pwr package)?
> 
> Thanks in advance, with all my best, erik S.
> 
> 
> 
> 
> =================================
> Erik-André SAULEAU
>  
> SEAIM
> Centre Hospitalier
> 87, Avenue d'Altkirch
> BP 1070
> 68051 Mulhouse Cédex
> Tel: 03 89 64 67 53
> Mel: sauleauea at ch-mulhouse.fr
> Web: www.ch-mulhouse.fr

The median test has low power and should be avoided.  For a validation 
study a hypothesis test is seldom of interest and you might base the 
sample size on the needed precision (margin of error; confidence 
interval width) of some estimate.

-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University