477 
Table 3. Investigation 1. Correlation Coefficient Between Blood Alcohol Con 
centration and Standard Deviation. 
Operator 
no. 
Date 
s 
X 
s 
y 
s 
p 
i 
11.2 
0.535 
0.672 
0.441 
13.2 
0. 199 
0.324 
0.590 
2 
12.2 
0.457 
0.070 
0.923 
18. 2 
-0.526 
-0.328 
0.018 
3 
12.2 
0.410 
0.094 
0. 167 
18.2 
-0.492 
-0.591 
-0.081 
4 
11.2 
0. 144 
11.2 
0.295 
13.2 
0.099 
13.2 
0.331 
deviations may be regarded as an estimate of a theoretical standard 
deviation only if the corresponding chi 2 -value from Bartlett’s test is 
not significant. In investigation 2 every operator measured with the 
same precision all day. 
The root mean square values of the standard deviations of the hori 
zontal parallax measurements for every day are plotted in diagram 1. 
The values of operator 3 were much lower during the last days due to 
training; unfortunately this experiment was the first time he had 
measured with an instrument of this type. Other operators also showed 
a similar but less evident effect of training. This dominated operator 3. 
This can be explained in the following way: after taking the alcohol 
the operator was more careful when setting the mark, knowing that he 
was under the influence of alcohol and that his results were being 
noted. This can also be applied to other operators as well. 
Correlation Between the Blood, Alcohol Concentration and 
Standard Deviation 
To investigate if there exists a linear relationship between the blood 
alcohol concentration and standard deviation of a setting in a stereo-