The purpose of this study is to construct the absolute scale of mental abilities developed by L. L. Thurstone on the basis of the raw scores of the Suzuki-Binet Intelligence Test given to 15, 820 children by Dr. J. Suzuki. The age of the children whose scores were used in this study ranged from 4 years to 12 years and 6 months, and they were classified into 18 age groups. The method of successive intervals developed by G. W. Diederich was applied in the course of scaling.It was assumed that the variable x, the mental ability required in solving the problems, was normally distributed for each age group, i, on the continuum with Mi as the mean and σi as the standard deviation. It was also assumed that there existed the critical value, tg, on the same continuum corresponding to each raw score, g, and that only those who had higher values of x than tg could get higher marks than g (see Fig. 1).However, in the course of analysis it was discovered that the assumption of normal distribution of x was somewhat inadequate and needed to be modified. The new distribution thus derived was much the same as normal distribution, but was slightly skewed to the right (see Fig. 4).The relationship among tg, Mi, σi and Z′ig, the deviate value of the new distribution corresponding to the distance from Mi to tg, is shown by the equation: tg=Mi+σiZ′ig. The values of tg, Mi and σi were obtained by the graphical solution developed by Diederich (See Fig. 5, Table 3 and Table 4).There was some variation in the values for t(g+1)-tg, but, where more than 30 children were available for obtaining a tg, the range of the variation was between .04 and .07 (see Table 3). This fact shows that the difference between the mental abilities required to get any 2 successive scores, g and (g+1), in the Suzuki-Binet Intelligence Test is almost the same regardless of the g value.From the values of Mi thus obtained the growth curve of intelligence was developed. It was slightly different from the growth curve obtained by Yokoyama and Indow (1), in which the absolute scale of the same data was constructed by using, as the landmark, the proportion of the right answers to each item of the test, though the amount of data available was 1/4 of that of the present study' the previous curve was almost a straight line while the present one proved to be slightly convex (see Fig. 6).As to σi as a function of age, a more remarkable difference was discovered between the results of the present study and those of the previous one (Yokoyama and Indow). In the previous study there appeared a tendency for the value of σi to become larger as the age increased. However, in the present study, no such tendency was discovered; the values of the standard deviation proved to be almost the same for all ages. The location of the absolute zero point, which was suggested by L. L. Thurstone, therefore, could not be determined from the results of the present study (see Fig. 7).
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