The letter most likely refers to Y Ahmavaara's 1954 article, Transformation analysis of factorial data and other new analytical methods of differential psychology with their application to Thurstone's basic studies, from Annales Academiae Scientiarum Fennicae.

In the letter, Thomson asks Ledermann to check if he is correct in his interpretation of the paper, referring to a chapter on m.v. selection in The Factorial Analysis of Human Ability, providing examples and working throughout.