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PubMed1988

Selecting candidates for a medical school: an evaluation of a selection model based on cognitive and personality predictors.

Two studies were conducted to attempt to evaluate the selection procedures used in Hadassah Medical School. The predictors assessed were the Israeli high school matriculation examinations, a general aptitude test, an interview and a semi-projective test designed to assess personality pathology. In the first study 145 students of the 1975 and 1976 cohorts were assessed, the criteria being a combination of peer evaluations, evaluation of supervisors and academic record. Results showed the matriculation average score to be the only effective predictor for all criteria. In the second study 155 students of the 1979, 1980 and 1981 cohorts were assessed, the criteria being evaluation of supervising doctors, BSc grades and grades during the clinical period. Results again indicated that the matriculation test is the most effective predictor. In this study, however, the other variables added to the prediction of criteria based on clinical evaluations. The results were discussed, raising several possible explanations for the relatively high validity of the matriculation scores. It was suggested the matriculation scores capture personality dimensions, such as motivation and adjustment to the learning environment, which are important factors for success in medical training.

Aptitude Tests↗
PubMed1992

Bayesian model selection and minimum description length estimation of auditory-nerve discharge rates.

Auditory-nerve fiber discharges are modeled as self-exciting point processes with intensity given by the product of a stimulus-related function and a refractory-related function. Previous methods of estimating these two functions, based on the maximum-likelihood principle, have the problem of estimating more parameters than the data can support. A new procedure, based on a Bayes criterion for choosing the complexity of the model in addition to estimating the parameters, solves the over-parametrization problem. This procedure is seen to relate asymptotically to Rissanen's minimum description length (MDL) criterion. A performance comparison of the MDL procedure with previous maximum-likelihood algorithms promotes the adoption of the MDL procedure for simultaneous estimation of the stimulus and recovery properties of auditory-nerve discharge.

Algorithms↗
PubMed1997

The evolutionary dynamics of selfish replicators: a two-level selection model.

The aim of the present paper is to study the evolutionary dynamics of selfish replicators in a constant genetic background. Selfish replicators are viewed as alleles at a single locus, having a pleiotropic effect. Infinitely many alleles are possible; they act on individual fitness and have various levels of ability to distort segregation. This results in a two-level process of selection, including inter-individual selection (effect on individual fitness) and intra-individual selection (ability to distort segregation). The model takes other parameters into account, such as dominance, inbreeding and inbreeding depression. The system can have two different behaviours. (1) In some cases, evolutionary cycles are possible. The cycles correspond to an alternation of phases with predominant inter-individual selection, corresponding to major-effect mutations, and phases with predominant intra-individual selection, corresponding to small-effect mutations. (2) For other values of the parameters, a synthetic fitness can be defined: this absolute allelic fitness is estimated as a function of one's fitness due to both inter-individual and intra-individual selection. During the course of evolution, the synthetic fitness increases. The optimisation of a synthetic fitness is the most general process. The optimised value is essentially homologous to the value optimised for resource allocation to male and female function in hermaphrodites (female function being homologous to the effect on individual fitness, and male function being homologous to distortion ability). The relative importance of both behaviours is discussed. It is argued that repeated sequences causing some human degenerative hereditary diseases may follow a two-step evolutionary process: a progressive increase in number of sequences accompanied by a decrease of the individual fitness would be followed by massive elimination of such sequences. But in general the optimisation of the synthetic fitness seems to be more likely.

Animals↗
PubMed2004

Modulation of the mouse testis transcriptome during postnatal development and in selected models of male infertility.

The aim of this study is to develop an overview of genetic events during spermatogenesis using a novel, specifically targeted gonadal gene set. Two subtracted cDNA libraries enriched for testis specific and germ cell specific genes were constructed, characterized and sequenced. The combined libraries contain >1905 different genes, the vast majority previously uncharacterized in testis. cDNA microarray analysis of the first wave of murine spermatogenesis and of selected germ cell-deficient models was used to correlate the expression of groups of genes with the appearance of defined germ cell types, suggesting their cellular expression patterns within the testis. Real-time RT-PCR and comparison to previously known expression patterns confirmed the array-derived transcription profiles of 65 different genes, thus establishing high confidence in the profiles of the uncharacterized genes investigated in this study. A total of 1748 out of 1905 genes showed significant change during the first spermatogenic wave, demonstrating the successful targeting of the libraries to this process. These findings highlight unknown genes likely to be important in germ cell production, and demonstrate the utility of these libraries in further studies. Transcriptional analysis of well-characterized mouse models of infertility will allow us to address the causes and progression of the pathology in related human infertility phenotypes.

Animals↗
PubMed1991

Automatic model selection for the 'best localization' of cardiac sources.

In the present paper a simulation study on the influence of noise and source model on the accuracy of localization of the sources of biomagnetic fields is presented. Applying a statistical analysis (F test) to the localization results obtained by various models on the simulated maps calculated using different theoretical sources and different noise levels we were able to define a 'best localization' (BL) method. It allows an automatic determination of the particular source model able to represent in the best statistical way a specific field distribution obtaining the best source localization for that distribution. We applied this method to the localization of cardiac sources in the experimental maps of the magnetic field produced by isolated rabbit hearts completely immersed in a conductive medium. The results clearly indicate that the proposed method is very effective in determining the 'best localization' for every particular field distribution while the use of the same source model for every field map often produces a source localization completely in contrast with the position of cardiac structures of the isolated hearts.

Animals↗
PubMed2004

AIC model selection using Akaike weights.

The Akaike information criterion (AIC; Akaike, 1973) is a popular method for comparing the adequacy of multiple, possibly nonnested models. Current practice in cognitive psychology is to accept a single model on the basis of only the "raw" AIC values, making it difficult to unambiguously interpret the observed AIC differences in terms of a continuous measure such as probability. Here we demonstrate that AIC values can be easily transformed to so-called Akaike weights (e.g., Akaike, 1978, 1979; Bozdogan, 1987; Burnham & Anderson, 2002), which can be directly interpreted as conditional probabilities for each model. We show by example how these Akaike weights can greatly facilitate the interpretation of the results of AIC model comparison procedures.

Bayes Theorem↗
PubMed1985

Cytometrically monitored neoplastic progression in the Nb bladder cancer model: selective proliferation of variant subpopulations.

The identification and understanding of neoplasm heterogeneity is essential to allow for more individually oriented treatment modalities. There is a tendency to limit the analysis of neoplasm heterogeneity to diagnostic classification only; however, recently refined methods of rapid subpopulation analysis should expand this restricted usage to monitoring of chemotherapeutic treatment. The documentation of the neoplastic progression of the Nb rat bladder cancer model as a function of variant subpopulation proliferation and selection is reported herein. This documentation represents the efforts of this laboratory to develop a flow cytometrically monitored animal bladder tumor model to evaluate the in vivo effects of chemotherapies on neoplastic subpopulations; particularly those subpopulations potentially metastatic or resistant to therapy. It is anticipated that this will increase our understanding of this model, and more specifically, tumor biology. This particular tumor initially occurred in an aged Noble male breeder rat.

Animals↗
PubMed1990

Global convergence properties in multilocus viability selection models: the additive model and the Hardy-Weinberg law.

A natural coordinate system is introduced for the analysis of the global stability of the Hardy-Weinberg (HW) polymorphism under the general multilocus additive viability model. A global convergence criterion is developed and used to prove that the HW polymorphism is globally stable when each of the loci is diallelic, provided the loci are overdominant and the multilocus recombination is positive. As a corollary the multilocus Hardy-Weinberg law for neutral selection is derived.

Genetics, Population↗