THE PERMANENCE OF INTERESTS 453 



year of college or professional school in my hundred individuals this 

 figure is, on the average 9, three fifths of the individuals showing sums 

 of from 6 to 12 for column 2 of Table 3. This average result of 9 may 

 be expressed as a coefficient of correlation or correspondence, such as 

 is in customary use to measure resemblances of various sorts. It is 

 equivalent to a correlation of over .60. This means that a person's 

 interests in the late elementary-school period resemble, in their order 

 and relative strength, the constitution of interests which he will have 

 eight years later to the extent of six tenths of perfect resemblance. For 

 the coefficient of correlation is a magnitude running from — 1.0, which 

 would be the coefficient if the sum of differences was 24, through 0, 

 which would correspond to a sum of differences of 16, to + 1.0, which 

 would correspond to a sum of differences of 0. A sum of differences of 

 8 means a resemblance greater than half of perfect resemblance, as the 

 reader expert in the mathematics of probability will realize. The sums 

 12, 10, 8 and 6, in fact, mean coefficients of resemblance or correlation 

 of -f .38, + .55 + .71, and + .83, respectively. 



The effect which the errors to which the original reports are subject 

 would have in making this obtained degree of permanence too high or 

 too low may now be considered. The chance errors — the mere failures 

 of memor}' or carelessness in report or inability to distinguish slight 

 differences in the interest of nearly equally interesting subjects — would 

 make the obtained estimate too low. Their action would be to change 

 the true sum of differences, whatever it was, toward 16, or the true 

 coefficient of correlation toward zero. The effect of errors of prejudice, 

 on the other hand, might have been toward so distorting memory and 

 observation as to make the order given for interests in the two later 

 periods more like the order given for the elementary-school period than 

 was in truth the case. This would, of course, unduly raise the obtained 

 estimate of permanence (that is, lower the sum of the differences). I 

 do not believe that such tendencies to read present interests into the 

 past and to leave the order reported for one period unchanged so far as 

 possible, are very strong, there being a contrary tendency to remember 

 and look for differences. On the whole, I should expect the effect of 

 the large chance errors in lowering the estimate of permanence to nearly 

 or quite counteract whatever balance of prejudice there may be in favor 

 of similarity of interests or projection of present conditions into 

 the past. 



A correlation of .6 or .7 seems then to be approximately the true 

 degree of resemblance between the relative degree of an interest in a 

 child of from ten to fourteen and in the same person at twenty-one. 



Consider now the difference between a subject's rank for interest and 

 its rank for ability at the same period. Using the same sample record 

 (Table 2) and assuming it to be a true record of the order of interests 



