The essentials of mental measurement . that the data are not homogeneous at all. The fit cannot be much improved by other assumptions as to the spread of the tail, several of which have been tried. The Type IV * The notation on this page is that of Elderton following Pearson, and the symbolsm, V, n and r have no connection with these symbols used elsewheie in the present book. 90 PSYCHOPHYSICS [PT. I curve itself is shown, contrasted with the pseudo-histogram, in Fig. mean (99-67), median (99-97) and mode (100-52) are worth com-pariDg, as a matter of iaterest, with the thresholds obtain
The essentials of mental measurement . that the data are not homogeneous at all. The fit cannot be much improved by other assumptions as to the spread of the tail, several of which have been tried. The Type IV * The notation on this page is that of Elderton following Pearson, and the symbolsm, V, n and r have no connection with these symbols used elsewheie in the present book. 90 PSYCHOPHYSICS [PT. I curve itself is shown, contrasted with the pseudo-histogram, in Fig. mean (99-67), median (99-97) and mode (100-52) are worth com-pariDg, as a matter of iaterest, with the thresholds obtained otherwise(see pp. 53, 60, 63 and 70). The reason for the bad fit in this case is, mathematically, the im-possibility of finding a curve to accommodate both the tall rectangle217, and the tail of 27, however the latter may be allocated. Much ofUrbans other data shows the same bad fit, and for the same reason, thesize of the tails. Not all however are bad. The best case is Subject II Mean = 99-67 grs-Mode 100-52 „Median = 99-97 „. 84 88 92 96 100 104 108 JKg. 12. A Type IV curve fitted to TJrbans data for Subject I, Jbeaviaranswers, in pseudo-histogram form (Urban himself) who had had much practice at this form of lighter answers in his case were as follows, compared (1) with acurve fitted by the Constant Process and (2) with a Pearson skew curve(here Type I). Urbans Subject II, Lighter answers Grams Observed p Normal Curve p Type I Curve p 84 •9333 •9604 •9432 88 •8622 •8640 •8520 92 •7000 •6767 •6875 96 •4489 •4456 •4627 100 •2311 •2320 •2379 104 •0956 •0922 •0858 108 •0156 •0272 •0187 On testing the goodness of fit we obtain For Normal Curve, P = Type I Curve, P = 0-91. CH. IV] SKEWNESS AND HETEKOGENEITY 91 Here the Gaussian is a good, and Type I an excellent fit. There is everyreason then to think that the data here are homogeneous. The bell-curve and pseudo-histogram are shown in Eig. 13. Since we have
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