[R] accuracy of measurements

[Denis Kazakiewicz]

Dear R people
Could you please help with following

Trying to compare accuracy of tumor size evaluation by different
methods. So data looks like

id true metod1 method2 ... 
1  2	2	2.5
2  1.5	2	2
3  2	2	2

etc.

Could you please give a hint how to deal with that.
Seems like {merror} does not suite to me because I am trying to compare
accuracy of measurements with their true known values not just overall
agreement of methods.
Moreover sample size is ridiculously small (33 patients) so ANOVA is not
much of help (or is it?)
Any suggestions, hints and even guesses are highly appreciated. I am
stuck a bit.