An analysis was made of the data on the cellular radiosensitivity of 79 organisms, compiled and published by Sparrow, Underbrink, and Sparrow in 1967, to determine whether there was statistical justification for considering these data as falling into eight distinct groups, each characterized by an almost constant value of absorbed energy per chromosome at D0. The 79 values of absorbed energy per chromosome were compared to sets of 79 random numbers generated with even probability over a log scale covering the same range. A parameter called "error" was defined to measure goodness of fit with the data arranged in eight groups. Error was calculated for Sparrow et al.'s data and for 5000 sets of random numbers. Of the 5000 random data sets, none had as small an error (as good a fit in eight groups) as did Sparrow et al.'s data. This finding was considered statistically significant, and it was, therefore, concluded that Sparrow et al. were correct in treating their data as eight groups.

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