[ RadSafe ] Statistics-evaluation of digital images

[Heike]

Dear Mr. Cedervall;

For a rating method with no  interval scaled values (meaning that 
equally spaced intervals on the scale can not be compared in a 
meaningful manner or e.g.  is an A average twice as good as a C 
average?) and a small sample size  , I would suggest  using a 
distribution free method ( non-parametric test) like the Wilcoxon- Mann 
Whitney test . This test should be available in any kind of statistical 
software package like systat , spss or etc.
Hope this information was helpful.

Regards;

Heike Ringeling
Stanford Dosimetry, LLC