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This work presents a number of very important contributions to the statistical treatment of mental environments. It grew out of the discussion concerning the existence and nature of general intelligence which has been going on since Spearman published his article on the “Proof and Measuement of Association between Things” in the American Journal of Psychology in 1904. This discussion culminated in Spearman's invention of the tetrad difference criterion. The present book of Kelley may be regarded as having its origin in the analysis of the work of Spearman.
It is of particular value in that it presents a new and ingenious method of handling the problem of detecting general and group factors underlying a number of variables or measurements. The symbolism which Kelley has developed has enabled him to present a clear simple proof of the tetrad criterion which is entirely independent of Spearman's demonstration. Not only has he given us an independent proof of the tetrad criterion but has laid down a series of sixteen propositions giving various criteria for the presence of group and general factors. Some of these will prove to be of distinct value.
A special technique is presented in the fourth chapter for determining what group factors are present in a set of tests. Unfortunately this technique is inadequately described so that it would be very difficult for any one to make use of it. Furthermore, it seems to be cumbersome in the extreme and incapable of utilization by one who might not have at his disposal a number of trained assistants.
It might be suggested that in future editions of this book it would be well to point out a clear distinction between group factors and general factors and to use the terms consistently throughout. The reader's attention should be called specifically to the fact that if the pentad criterion holds, it does not mean that two general factors are present, but only that there are not more than two general factors or more than one general plus