A comparison of the logistic risk function and the proportional hazards model in prospective epidemiologic studies.
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No statistically significant associations were found between ABO blood group distributions and RDC subtype diagnoses in 79 subjects with unipolar (single episode and recurrent) and bipolar major depressive disorder using data from our sample. We discuss methodological issues related to the control samples and choice of statistical methods in the reported studies which have looked for associations between ABO blood types and patients diagnosed as having an affective disorder. After presenting our rationale for employing the logarithm of the cross product ratio (lambda) in place of the more traditionally utilized chi-squared, we used lambda to reanalyze the original data from nine studies in the literature. The individual studies are equivocal on the basic issue of an association between type O blood and bipolar I illness, either compared to controls or to recurrent unipolar patients. The combined (weighted average) measure of association indicates a small but definite association, but statistical analysis of the dispersion of the individual estimates around this combined estimate reveals that the studies have a higher degree of heterogeneity in results than expected by chance. The consequences of this finding are discussed, and possible explanations are offered.
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ESS germination strategies are studied in a model of annual plant population dynamics in a randomly varying environment. The possible strategies are different values of the annual germination fraction G, either constant over time or varying in response to a "cue" correlated with upcoming environmental conditions. The model generalizes D. Cohen's model (1966, J. Theor. Biol. 12, 119-129; 1968, J. Ecol. 56, 219-228) by allowing density-dependent per capita seed yields. ESSs are characterized in terms of the resulting harmonic mean growth rate of population density. The ESS criterion cannot be solved analytically, but qualitative relationships between the value of the ESS and other population parameters are obtained, and environments in which 100% germination is an ESS are identified. Some explicit predictions of the theory are summarized and compared with ideas of M. Westoby (1981, Amer. Nat. 118, 882-885). The results of this study are compared with those of Cohen (op. cit.) in a companion paper.
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The present study investigates the psychometric adequacy of a self-report inventory of depression (the QD2) with respect to the severity of depressive symptoms, within the framework of a unidimensional model of depressive states. Responses to the 52 QD2 items, by 481 subjects divided into four groups (depressed, psychiatric, somatic and control), were subjected to a Rasch analysis. Results show that 15 items (QSD(R1] display a satisfactory goodness of fit for both items and persons, as defined by the Rasch model. This set of items, solely related to 'pure' depression, gives a measure of the severity of depression, free from anxiety symptoms. The discussion focuses upon the advantages of the Rasch model as compared to traditional tests. The Rasch 15-item solution should provide a parsimonious tool for future studies on the classification of depressive disorders.
"A multinomial logit model focusing on economic and other locational factors is formulated and applied to data on place-to-place migration in Israel. Results indicate the effects of expected industrial wage differentials, in accordance with the hypothesis of Harris and Todaro (1970), and of disparities in the structure of industrial employment, suggesting that perceived risk as well as expected return enter into the decision to migrate, as Stark and Levhari (1982) have argued. Other effects include those associated with regional differentials in amenities and agglomeration associated with urbanization, population mobility by age group, center-periphery migration trends, border security hazards, and the like. Implications of the analysis for the Israeli policy of population dispersion are discussed."
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Operations research techniques are being used to solve business and government problems throughout the world. This paper discusses the use of an analytical technique--the location set covering algorithm--to determine placement of medical supply centers in Ecuador. By establishing the optimum location of supply centers it is possible to effectively utilize scarce health care resources in a developing country and to help community level health workers be better prepared to deliver primary health care services.
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