If we may take the habits, attitudes and utterances of people of low mentality and little independence and originality as evidence of a primitive type of thinking and those of thoughtful people as evidence of a more highly developed type, we can expect to find in comparative sociology the mental distinctions that characterize primitive and more highly developed peoples. If we compare the initial stages of a mental discipline with the later stages we can find evidence of the same distinctions. If we examine the mental processes of everyday life which require little effort and which we can engage in in indolent moods and compare with those that are distinctly effortful and which, as we perform them, carry the thrill of awakeness and vitality, we again find evidence of the same distinctions. In each of these comparisons the more primitive thought is largely in terms of broad categories and its decisions are unambiguous, unqualified and lead to unquestioned conclusion, while the higher type is either definitely quantitative or concerned with much finer categories and leads to qualified conviction and tempered judgment.

The intercorrelations of thirty-seven variables, including the Minnesota battery of “mechanical ability” tests, the seven MacQuarrie tests of “mechanical ability,” O'Connor's Wiggly blocks, and the Stenquist picture-matching test, were analyzed by Thurstone's centroid method. Five factors, Perceptual, Verbal, Youth, Manual Agility, and Spatial, were taken out. Factors prominent in so-called mechanical ability tests are the Spatial and Perceptual ones with Mac-Quarrie's dotting test significantly high in the Manual Agility factor. Each of the factors can be measured with group pencil-and-paper tests.

Delinquent boys are compared with non-delinquents with respect to their attitudes towards a series of “good” and “bad” social acts, by the use of scales having rational origins of measurement. A new technique, essentially an extension of Thurstone's Method of Successive Intervals, is found to give results similar to Horst's Method of Balanced Values. Significant differences in mean attitude between the two groups are not found.

It is shown that invariance requirements remove the indeterminacy in factor determination and lead to an integration of factorial studies with promise of considerable reduction in computational labor. The selection of significant primary factors is discussed, with special reference to Thurstone's simple structure criterion.

It is shown that by making the assumption that the knowledge of the test-item and the knowledge of the entire test are both distributed normally, the correlation coefficient between any item and the entire test can be expressed as a function solely of two proportions — the percentage of a high-scoring group passing the item and the percentage of a low-scoring group passing the item. This function is expressed graphically as a family of curves for each of two conditions — where the high-scoring and low-scoring groups are samples of the highest and the lowest quarters respectively, and where they are samples from the upper and lower halves. It is shown, moreover, that two other common measures of item validity, the upper-lower difference and the critical ratio of the upper-lower difference, may be drawn on the same coordinate axes.

The assumption of specific operation times leads to equations similar to those which are the basis for a factor analysis but in which the time scores replace item scores. An analysis of time scores is shown to lead to results equivalent, in a first approximation, to those obtained from an analysis of item scores. It is suggested that by modifying the factor technique it may be possible to use additional information to check with the results from an analysis.