Includes a reprint of Thomson's letter titled Methods of Estimating Mental Factors from Nature, vol. 141, (Feb 1938), 246; a handwritten copy of Thomson's manuscript in Ledermann's hand titled Copy of Professor Thomson's M S on regression and Bartlett's estimates; and a typed copy of a letter from Bartlett to Thomson in which argues that neither he nor Thomson are right and the other wrong, but rather that both of their methods are valid under the right circumstances.