Over the period of 5 years 1976-1980, total of 4, 042 cases of accidental injuries serious enough to prevent the employees from their works at least 4 days occurred among the workers of six types of industrial enterprises, land carriage, forestry, tranportation, construction, manufacture and other business, under the jurisdiction of Kagoshima Labor Standard Office. In these cases, the number of those who had at least one accident was 3, 840, of whom 3, 646 was injured only once, 163 twice, 25 three times and 3 four times. Assuming that the distribution for the frequency of accidents per head of those who had at least one accident is a truncated Poisson distribution, the incidence rate of accidents for the hypothetical population at risk of accidents can be estimated by trial and error as the unknown parameter m of the equation y=m/1-e-m, where y is the average frequency of accidents per head of those who had at least one accident. We obtained here a value of 0.113 for all the industrial enterprises involved, the highest being 0.269 for forestry followed by 0.163 for construction and the lowest 0.064 was for manufacture. Thus, the number of working population at risk of accidents was obtained as a simple quotient of the total number of accidents divided by m, being 35, 799 for all the industrial enterprises involved, 4, 783 for land carriage, 1, 173 for forestry, 2, 009 for transportation, 3, 394 for construction, 13, 815 for manufacture and 17, 327 for the other business. If the total cases of accidental injuries are randomly derived from the workers at risk of accidents, then the distribution for the frequency of accidents per head containing the class 0 should conform to the complete Poission series. However, the fitted values for the Poisson distribution indicated a poor agreement which was born out by the high value of x
2, the x
2 was 64.21 on 2 degree of freedom for all the industrial enterprises involved, for which p<0.005. On the every year basis, however, the distribution for the frequency of accidents per a worker conformed to the Poisson series. From the facts described above, we may conclude that the industrial accident is an unusual event and every worker is not always equally exposed to the risk of accidents even in the same working condition.
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