372 Pigmentation, Selection and Anthropometric Characters 
probable error here referred to was obtained in the following way. The formula 
for the probable error of the mean 67449 -7= was used ; a was taken in each case 
F VA 
to represent the standard deviation of the mean of the whole, while N was the 
total of each hair colour group. Thus instead of calculating the probable error ot 
each mean in the usual manner, the probable error of each mean with reference to 
the mean of the whole is obtained. This gives the easiest method of estimating 
the value of the separate means from the mean of the whole. Lines have been 
drawn in each table to mark twice the probable error thus calculated. On looking 
at Figure I A it is clear that the only group which need occupy our attention is 
that of the dark brown hair. All the other means fall well within the line repre- 
senting twice the probable error ; but the mean of the dark brown hair group 
stands outside it. A line representing four times the probable error would include 
it, and, therefore, the deviation is not a very serious one ; on this evidence alone it 
Hair Colour . 
Red 
Fair 
Light Brown Medium Broiun Bark Brown 
Black 
144-5 : 
Boys 
✓ 
s 
144-0-; 
/ 
143-5^ 
143-0- 
142-5-H 
\ 
142-Ch 
14 1-5-^ 
\ 
\ 
N 
N 
\ 
\ 
141-0- 
N 
N 
Twice p. e. 
Mean of whole 
Mean of Hair 
Colour group 
Twice p. e. 
Fig. I. Age 13. 
Hair Colour and Height. 
