Abstract. The hypothesis put forward for discussion is that, among normal persons, differences in “intelligence” (i.e., innate general cognitive ability) are determined by a large number of genes, segregating in accordance with Mendelian principles and each producing effects that are small, similar, and cumulative. From these assumptions, with a due allowance for dominance and assortative mating, formulae are derived for the correlations to be expected between siblings, parents and offspring, and remoter relatives. Data from school surveys yield coefficients which are in almost complete agreement with the theoretical figures thus deduced. An attempt is also made to analyse the variance of the assessments obtained, and to estimate the contributions of genetic factors and non‐genetic factors respectively. Appreciable differences are found between the results obtained from raw measurements based directly on intelligence tests and those obtained from revised or adjusted assessments based on all the available evidence. With the former nearly 25 per cent. of the variance is apparently due to non‐genetic factors; with the latter barely half that amount.

No abstract

Thés material was produced from a microfilm copy of the original document. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the original submitted. The following explanation of techniques is provided to help you understand markings or patterns which may appear on this reproduction. 1.The sign or "target" for pages apparently lacking from the document photographed is "Missing Page(s)". If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting thru an image and duplicating adjacent pages to insure you complete continuity. 2. When an image on the film is obliterated with a large round black mark, it is an indication that the photographer suspected that the copy may have moved during exposure and thus cause a blurred image. You will find a good image of the page in the adjacent frame. 3. When a map, drawing or chart, etc., was part of the material being photographed the photographer followed a definite method in "sectioning" the material. It is customary to begin photoing at the upper left hand corner of a large sheet and to continue photoing from left to right in equal sections with a small overlap. If necessary, sectioning is continued again-beginning below the first row and continuing on until complete. 4. The majority of users indicate that the textual content is of greatest value, however, a somewhat higher quality reproduction could be made from "photographs" if essential to the understanding of the dissertation. Silver prints of "photographs" may be ordered at additional charge by writing the Order Department, giving the catalog number, title, author and specific pages you wish reproduced. 5. PLEASE NOTE: Some pages may have indistinct print. Filmed as received.

No abstract

The original formula for rescaling estimates and test‐scores was derived from the three basic assumptions used by Galton and Pearson when deducing their formulae for the correlation coefficient; but it makes no allowance for differences in reliability and validity. However, the various modifications since suggested appear to rest on highly speculative arguments, and the improvements so obtained are seldom large enough to be statistically significant. On the basis of actual trials with tests and estimates of average validity, assessments of the predictive accuracy to be expected with the original formula have been computed. The accuracy diminishes progressively with the time‐interval involved, but remains high enough to justify its use for the practical purposes of the educationist.