34 Effect of Alcohol on Psycho-Physiological Functions. 



which would produce a much larger P. E. u than would result, other 

 things being equal, from series of 25 reactions each. 1 



The "certain cause" indicated by a probable correctness of 1.000 is 

 of course not synonymous with specifying that cause as a 30 c.c. dose of 

 alcohol. Any difference between two averages may be produced by 

 one cause, but more likely by several factors, the resultant of which 

 changes the phenomena under observation. In these experiments it 

 was naturally the aim to make the alcohol dose the critical change and 

 cause. While the probable correctness supplies an estimate of the 

 reliability of particular differences in results as being produced by some 

 change or other, it is not by itself a measure of success in isolating the 

 alcohol effect. 



The mean variations (M. V.) are included in table 2 in parallel col- 

 umns with the averages to which they apply. The differences are com- 

 puted for these exactly as was done for the averages (see p. 32). In 

 section in of the table, the effect of alcohol upon the M. V. is found to 

 produce +11 and +7crin periods 2 and 3, an increase in the variability 

 of the reaction time following the dose, while period 4 shows a decrease. 



It should be borne in mind that the plus and minus signs are employed 

 in their usual meaning throughout this monograph. For example, a plus 

 (+) difference or percentage means a longer reflex time, a larger ampli- 

 tude, a larger number of finger-movements, a larger number of elec- 

 trical units required for threshold stimulation, a larger variability be- 

 tween measurements, etc., whereas the minus (— ) sign in these same 

 connections would have the reverse meaning. The effect of alcohol 

 must, of course, always be interpreted according to the nature of the 

 measurement; e. g., a + reaction-time percentage (slower reactions) 

 would not ordinarily be associated with a + percentage for finger 

 movements (faster movements). 



It will be seen by consulting Dodge and Benedict's report, page 29, 

 that they computed the average difference (Av. D.) of the day's meas- 

 urement according to the formula 2 



^ (1 -2) + (1-3) + (1-4) + (!-*) 



Av. D.= 



n 



According to our method for determining the differences outlined in 

 previous paragraphs, the formula for Av. D. would be: 



(2-l) + (3-l) + (4-l) + (n-l) 



Av. D= 



n 



1 This condition of a small n (5 eye reactions, 10 patellar reflexes, 4 lid reflexes, etc., taken 

 within any one period) is operative throughout all our measurements and increases the size of the 

 probable errors. The usual method of obtaining the P. E. M for the 3-day averages for any period 

 has been to find the P. E. M for each of the three values which are averaged. The sum of the_three 

 P. E M is divided by three to obtain the typical P. E. M ; then the result is divided byV3, since 

 the n for the three averages together is three times as large as for one. 



2 It is obvious that n in their formula refers to the number of experimental periods following 

 and excluding the first period, or normal of the day. 



