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Biomedical subjects

J Wittes

Publications and source records attributed to J Wittes.

58 records · Page 4Linked to original sources
PubMed1977

Relation of birth order, family size and social class to psychological functions.

Findings are reported on birth-order and family-size effects for five psychological functions measured by the military preinduction test battery which was administered to a total population of 19-yr.-old Dutch men. These men were born between 1944 and 1946, were members of 1- to 6-child families and were from the two major social classes. A clear birth-order gradient was present on all test measures for both social classes. Family-size effects, however, differed by social class. The results extend to a range of psychological functions the findings previously reported for a single test of non-verbal intelligence, suggesting that family-structure variables play a role in understanding intellectual development.

Adult↗
PubMed1975

Spontaneous abortion as a screening device. The effect of fetal survival on the incidence of birth defects.

To make sound inferences about the distribution, causes and risks of congenital anomalies requires an understanding of selective survival among fetuses. Studies of spontaneous abortions are therefore advocated. A simple model is proposed of the distribution, among spontaneous abortions and births, of conceptuses with and without anomalies. The resulting equation accomodates both maternal and fetal factors. Interaction between maternal and fetal factors is hypothesized, in the form of a maternal device for screening out anomalous conceptuses. A number of the known facts about congenital anomalies are shown to be plausibly interpreted in terms of the proposed model. Finally, some clinical and epidemiologic implications of the model for the study of spontaneous abortions are pointed out.

Abnormalities, Drug-Induced↗
PubMedDate not supplied

The role of internal pilot studies in increasing the efficiency of clinical trials.

Investigators often design clinical trials without knowing precisely the values of such necessary parameters as the variances or the event rates in the control group. In order to determine reasonable values for such parameters, they may design a small pilot study external to the main trial. In this paper we propose designs, which we term internal pilot studies, that designate a portion of the main trial as a pilot phase. At the end of the internal pilot study, the investigators recompute preselected parameters and recalculate required sample size. The study then proceeds with the modifications dictated by the internal pilot. Final analyses of the results incorporate all data, disregarding the fact that part of the data came from a pilot phase. As one example of this type of design, we consider a study to compare two normally distributed means. By simulation, we show a numerical example for which the effect of the procedure on the alpha-level is negligible, but the potential gain in power considerable. We urge considering a similar approach for a number of types of endpoints.

Pilot Projects↗