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E. C. MACDOWELL AND E. M. VICARI 



meaning from the variability in the other data. In both time 

 and perfect trials the variability is controlled by the high vari- 

 ates, since the low variates are limited by the physical possibili- 

 ties of speed in time, and in perfect trials, by the absence of a 



FREQUENCY DISTRI BUTIONS OF 



NUMBERS 

 OF RATS 



FHE NUMBER OF PERFECT TRIALS 



TESTS CONTROLS 



TEST AVERAGES ^ CONTROL AVERAGES 1 



8765 4 3210 



NUMBER^ OF PERFECT TRIALS 



Fig. 15 Frequency distributions of the numbers of perfect trials made by 

 each rat. Units on the vertical scale are numbers of rats, units on the base line 

 are numbers of perfect trials. In order to keep inferiority at the right as in pre- 

 ceding charts, the scale reads from right to left. Broken line shows the tests; 

 solid line, the controls. 'Completes' and 'incompletes' are used, with males 

 and females in all strains together. 



single perfect trial. A larger number of high variates, i.e., 

 greater variability, is associated with inferiority in time; in 

 perfect trials, with superiority. 



b. The number of trials before the first perfect trial. The number 

 of trials before the first perfect trial is a further basis for com- 

 parison of the tests and controls. Table 21 gives the average 



