Impact of corrections for dynamic selection bias on forecasts of retention behavior

We investigate the impact of corrections for dynamic selection bias on forecasting accuracy in a multi‐period stay/leave model. While corrections for selection bias are needed for consistent coefficient estimates, they do not necessarily produce more accurate forecasts than uncorrected techniques. Theorem 1 shows that, apart from estimation errors, a shrinkage principle applies: the heterogeneity restriction imposed by uncorrected and combination techniques improves accuracy for forecasting individuals that leave, and hurts accuracy for forecasting individuals that stay. This has important implications for decision making because of the potential for asymmetric losses. We also present an illustrative empirical application and results from Monte Carlo experiments. We find that differences in relative accuracy vary directly with the degree of selection bias and inversely with the percentage of the initial population that stays. Copyright © 2007 John Wiley & Sons, Ltd.     

Specification versus data fitting: SEM prediction and the Q‐class estimator

We propose a new class of limited information estimators built upon an explicit trade‐off between data fitting and a priori model specification. The estimators offer the researcher a continuum of estimators that range from an extreme emphasis on data fitting and robust reduced‐form estimation to the other extreme of exact model specification and efficient estimation. The approach used to generate the estimators illustrates why ULS often outperforms 2SLS‐PRRF even in the context of a correctly specified model, provides a new interpretation of 2SLS, and integrates Wonnacott and Wonnacott's (1970) least weighted variance estimators with other techniques. We apply the new class of estimators to Klein's Model I and generate forecasts. We find for this example that an emphasis on specification (as opposed to data fitting) produces better out‐of‐sample predictions. Copyright © 1999 John Wiley & Sons, Ltd.     

Intracellular cytoskeletal elements and cytoskeletons in bacteria

Within a short period of time after the discovery of bacterial cytoskletons, major progress had been made in areas such as general spatial layout of cytoskeletons, their involvement in a variety of cellfunctions (shape control, cell division, chromosome segregation, cell motility). This progress was achieved by application of advanced investigation techniques. Homologs of eukaryotic actin, tubulin, and intermediate filaments were found in bacteria; cytoskeletal proteins not closely or not at all related to any of these major cytoskeletal proteins were discovered in a number of bacteria such as Mycoplasmas, Spiroplasmas, Spirochetes, Treponema, Caulobacter. A structural role for bacterial elongation factor Tu was indicated. On the basis of this new thinking, new approaches in biotechnology and new drugs are on the way.     

Spontaneous activity of rats on diets varied in protein,carbohydrate and fat content

Résumé Nous avons mesuré l'activité spontanée de rats mâles et femelles recevant des rations contenant 10%, 25% et 60% de protéine et 29% de graisses non-saturées ou 31% de graisses saturées. Les rats ont été maintenus isolés dans des cages à stabilimètre 6 jours de suite. On a comparé les données obtenues pendant les 3 derniers jours. On n'a pas trouvé de différences significatives dans l'effet des différents régimes, ni pour les mâles ni pour les femelles.

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This work was supported in part by a grant from the National Institute of Neurological Diseases and Blindness, No. NB 01941, of the National Institutes of Health, U.S. Public Health Service, Bethesda, Maryland, and the Fund for Research and Teaching of the Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts.     

Endogenous glucose release stimulated by oral sucrose administration in rats

Résumé On a examiné l'élevation de la glycémie chez les rats des 2 sexes après administration orale de sucrose. Une sécrétion de glucose semble prendre place en même temps que l'absorption de cette substance. On suggère un mécanisme basé sur l'interaction du glucagon, du glucose-6-phosphate et de l'insuline suivant l'administration de sucre. Les expériences témoins semblent éliminer la possibilité que ces résultats soient dus au stress.     

Prostaglandins and food intake of rats

Zusammenfassung Nachweis der Wirkung verschiedener Prostaglandine auf die Nahrungsaufnahme bei der Ratte.

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This work was supported in part by grants-in-aid from the National Institute of Neurological Diseases and Blindness No. NB-01941 and the National Institute of Arthritis and Metabolie Diseases No. AM-02911; and the Fund for Research and Teaching, Department of Nutrition, Harvard School of Public Health.