"Hitherto the literature of mental and physical tests has been scattered in numerous journals; the results obtained by different investigators have too often not been compared; indeed, in many cases where the methods have been divergent, comparison has been impossible. In consequence, there have been no recognized standards of procedure and none of performance. Nevertheless, I believe that the time has now come for the taking of an account of stock, and for the systematization of the available materials. This conviction, which is the outgrowth of my own interest in the experimental study of mental capacities, an interest that has been with me during the past ten years, has been confirmed by many suggestions from colleagues and friends, who have pointed out that a manual of directions for mental tests would meet a real need, and might further the cause of investigation. I began, in March, 1906, to prepare a small handbook of mental tests. The impossibility of adequate treatment of the subject in small compass has, however, necessitated the expansion of that early undertaking into the present work. In the introductory sections of the volume, I have sought to show the general purposes of mental tests, to lay down rules for their conduct, and to explain the methods of treating data. In this connection I discuss the calculation of measures of general tendency, measures of variability, indexes of correlation, and other statistical constants. In the body of the volume, I have brought together, for specific treatment, some fifty of the most promising tests. In every case, my plan has been to sketch the development of the test, to prescribe a standard form of apparatus and method of procedure, to explain the treatment of the data secured, and to set forth the results and conclusions thus far obtained. The tests that I have selected may not prove, ultimately, to be those of most value, but they are, I think, numerous enough, and varied enough in type, to furnish a working basis for investigations for some time to come"--Pref. (PsycINFO Database Record (c) 2005 APA, all rights reserved).