The essentials of mental measurement . of the abovecurve for the purpose of drawing it, are best performed in tabularfashion. For example, the present calculation might be arranged asfollows, and the reader should calculate one or two ordinates for practiceby this means. (a) (6) (0) (d) (e) (/) a;-60-13 2 Xl-SS Column cX loge Reciprocal ofAntilog. column d 29 Lolunm c X J gg^^g^j y This arrangement is suitable for an approximate calculation usinga ten inch slide rule, from which the logarithms are also taken. The CH. II] THE ELEMENTARY THEOEY OF PROBABILITY 43 accuracy thus attained is quite a
The essentials of mental measurement . of the abovecurve for the purpose of drawing it, are best performed in tabularfashion. For example, the present calculation might be arranged asfollows, and the reader should calculate one or two ordinates for practiceby this means. (a) (6) (0) (d) (e) (/) a;-60-13 2 Xl-SS Column cX loge Reciprocal ofAntilog. column d 29 Lolunm c X J gg^^g^j y This arrangement is suitable for an approximate calculation usinga ten inch slide rule, from which the logarithms are also taken. The CH. II] THE ELEMENTARY THEOEY OF PROBABILITY 43 accuracy thus attained is quite as great as the extent of the experimentjustifies. If logarithm tables, or calculating machines, were to be used,somewhat different tabular arrangements would be required. Some of the calculation in the above table has, however, once andfor all been done and printed in tables of the probability curve. Thebest of these for our purpose is Sheppards table, printed as Table IIn Professor Pearsons Tables for Statisticians and 56 57 58 59 60 61 MillimetresFig. 6. A normal curve fitted to the bisection histogram is also shown Fitting a Normal Curve to the Bisection Data with theAid of Sheppards Tables* I II III IV V X in mms. a;=a;-60-13 Sheppards xa;71-38 Sheppards z y=:29z/l-38 6013 60 59-5 59 58-5 58 57 66 0 013 0-63 113 1-63 2-13 313 413 0 009 0-46 0-82 1-18 1-54 2-27 2-99 •3989432 •397 •359 •285 •199 •122 •030 •005 8-388^347^545994^182^56063Oil The other half of the curve can be drawn by symmetry. No interpolation is here used inthe tables. A slide rule, or Crelles Calculating Tables, can be used for the multiplications. * Of course an experiment of only 29 observations does not justify any curve fittingat all, as the accuracy is not sufficient, the sample not being large enough. But a shortexample is necessary for explanatory purposes in a text-book. 44 PSYCHOPHYSICS [pt. i We are at present only concerned with Sheppards first and fifthcol
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Keywords: ., boo, bookcentury1900, bookdecade1920, booksubjectpsychophysiology
