6 BULLETIN 839, U. S. DEPARTMENT OF AGRICULTURE. 



PERSONAL EQUATION VARIATION. 



COUNTING THE SAME SLIDES ON DIFFERENT DAYS BY ONE ANALYST. 



Table 1 gives actual duta obtained from counts made by each of 

 two analysts working upon' three slides which were prepared from the 

 same bulk sample and upon which they made two counts on each of 

 three successive days. 



Table 1, — Results of counts of same slides by two analysts on different days. 



Date. 



Slide. 



Analyst. 



Count 

 No. 



Bran 

 particles. 



Hairs. 



Total, 



1918. 



A 

 A 

 B 

 B 

 C 

 C 

 A 

 A 

 B 

 B 

 C 



c 



A 



A 

 B 

 B 

 C 

 C 

 A 

 A 

 B 

 B 

 C 

 C 

 A 

 A 

 B 

 B 

 C 

 C 

 A 

 A 

 B 

 B 

 C 

 C 





1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 

 1 

 2 



87 

 92 

 60 

 60 

 87 

 81 

 103 

 114 

 86 

 80 

 90 

 87 

 76 

 82 

 60 

 49 

 62 

 64 

 100 

 96 

 85 

 77 

 89 

 83 

 80 

 83 

 49 

 53 

 60 

 77 

 104 

 106 

 78 

 77 

 86 

 86 



59 

 64 

 60 

 58 

 62 

 74 

 58 

 52 

 64 

 58 

 62 

 57 

 66 

 69 

 55 

 48 

 66 

 68 

 54 

 56 

 52 

 55 

 65 

 59 

 65 

 66 

 61 

 57 

 66 

 71 

 54 

 55 

 55 

 55 

 65 

 62 



146 



Do.. 



do 



156 



Do.. 



do 



120 



Do.. 



do 



118 



Do.. 



do 



149 



Do.. 



do 



155 



Do.. 





161 



Do.. 



do 



166 



Do.. 



do 



150 



Do.. 



do 



138 



Do.. 



do 



152 



Do.. 



do 



144 



Jan. 8 





142 



Do.. 



do 



151 



Do.. 



do 



115 



Do.. 



do 



97 



Do.. 



do 



128 



Do.. 



do 



132 



Do . 





154 



Do.. 



do 



152 



Do.. 



do 



137 



Do.. 



do 



132 



Do.. 



do 



154 



Do.. 



do 



142 







145 



Do.. 



do 



149 



Do.. 



do 



110 



Do.. 



do 



110 



Do.. 



do 



126 



Do.. 



...do 



148 



Do.. 





158 



Do.. 



do 



161 



Do.. 



do 



133 



Do.. 



...do 



132 



Do. 



do 



151 



Do.. 



do 



148 









For the purpose of emphasizing certain salient points, the results 

 recorded in Table 1 have been rearranged in Table 2, in considering 

 which it is necessary to regard the different portions carefully. 

 Keenan's greatest variation in two counts of bran particles on a 

 given slide on any one day was 17 points (slkle C, Jan. 9, 1918), 

 while Lyons' greatest variation was 11 points (slide A, Jan. 7, 1918). 

 In the matter of counting hairs the greatest variation in the counts 

 obtained on a given slide on any one day by Keenan was 12 points 

 (slide C, Jan. 7, 1918), while Lyons' greatest similar variation was 6 

 (in several instances). In these cases it appears therefore that the 

 personal variation due to the error of counting probably would not 

 exceed 17 points in the case of particles or 12 points in the case of 

 hairs. 



