An Edgeworth series was fitted to an experimental 

 curve using the parameters calculated by this method, to 

 insure that they were good estimates to the extent that they 

 provided a good fit to the data. Figure 13 is the trace of 

 an experimental curve of random noise which shows con- 

 siderable skewness. The fit of an Edgeworth series ap- 

 proximation to the experimental curve is seen to be very 

 good. 



0.5 



f(x) 



0.4 



0.3 



<c 0.2 



0.1 



EXPERIMENTAL PD 



THEORETICAL 

 NORMAL 



-2 -1 



AMPLITUDE 



1 2 



IN STANDARD DEVIATION UNITS 



Figure 13 . Ex pe r iment al PD curve of random noise showing 

 considerable skewness. The points shown are calculated 

 us ing Ed g ewo rth ' s series with the moment s calculated from 

 the curve itself by the method of moment s described in the 

 test. A theoretical normal curve is shown for comparison. 



The chi-square test was performed on a few selected 

 curves and the results are shown in table 5. An X marks 

 those noise samples for which \ a was equal to or greater 

 than 49. 6, which is the tabulated value of \ 3 for 29 degrees 

 of freedom at a 1 per cent probability level. The value of 

 X s is given for the samples for which the hypothesis was 

 not rejected by the test. The figure also shows whether 



34 



