[R] Q: Mean, median and confidence intervals with functions "summary" & "boxplot.stats"

Uwe Ligges ligges at statistik.uni-dortmund.de
Thu Aug 30 11:57:10 CEST 2007

Tom Willems wrote:
> Dear R ussers,
> My question is, " How can my mean be outside the confidence intervals ?!"
> I think i have the answer for it, but i would like to hear some other 
> ideas on it.
> First my data is not continuose but categorical, it is a titre calculated 
> on a dilution serie.
> It is stored as a column of values, and a column indicating the phase of 
> the trail.
> Theoreticaly it is possible to have a value ranging from 0 to 4, but in 
> practice, only sertain values will occure, and they will repeat.
> So it are frequencies.
> This is why i belief that it is better to work with a median than with a 
> mean, because it represents the cluster of values wich occure most.
> Below I only give one example, but the mean being below the lowest 
> confidence limit occures several times over different tests.
> does my answer seam reasonable, or should i perhapes use an other methode, 
> any sugestion?
>         summary_1d  = summary(subset(eda_data,  phase=='1' & test=='test 
> 1' ,select=lg_value), na.rm = T)
>         conf_1d  = boxplot.stats(subset(eda_data,  phase=='1' & 
> test=='test 1' ,select=lg_value))
>         Mean            Median             95% Confidence     Int. StDev.  
> Variance
>         1.198            1.681                   1.441 >  < 1.922 0.931    
>    0.866

I do not understand which "confidence" has been calculated? Based on 
which assumptions / data? Is it pointwise or not? We need much more 
information - and if you think it is a problem with R or usage of R 
functions, then please give us a reproducible example.

Uwe Ligges

> Kind regards,
> Tom W.
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