sh_ and ch_ compose the same words

[Torsten]

Torsten is correct in stating that the calculation of R assumes that the data is normally distributed. 

I would love to see a reference for that.

See "You are not allowed to view links. Register or Login to view." (Charles J. Kowalski 1972). Skip to the very short conclusion at the end of the paper for a summary.

This doesn't mean that the sampling data distribution requires normality if the samples are large enough and therefore represent the real world data. The reason for that is You are not allowed to view links. Register or Login to view.. In this way it is possible to assume that the frequencies for all 'ch'/'sh' words are representative for all the words in the Voynich manuscript.