[R] calculating/plotting error ellipses

[Jan M. Wiener]

Hello,
thank you very much for the quick answer.
This works well. it draws a nice ellipse in the right orientation.
However, I  doubt that the ellipse represents the 95% confidence
interval, even if that is the standard-parameter for level is .95. The
ellipse surely is to large?
Any further help would be greatly appreciated.
Best,
Jan


bbolker wrote:
>
> Jan M. Wiener wrote:
>   
>> hello,
>> sorry for posting what may be a simple question:
>> i do have a matrix of coordinates (positional judgments, see below) and
>> now want to calculate and plot the corresponding error ellipse.
>> can anyone help me with the exact steps/syntax?
>>
>>     
>
> Something along the lines of:
>
> m = colMeans(xyDat)  # calc. column means
> v = var(xyDat)             # compute var-cov matrix
> library(ellipse)              # you may need install.packages("ellipse")
> first
> plot(ellipse(v,centre=m),type="l")   ## draw the confidence ellipse
> points(m[,1],m[,2])     # add the cent(re|er) point
>
>   Of course, I haven't actually tested this ...
>
>   Ben Bolker
>
>