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At least 595 records · Page 33Linked to original sources
PubMed1998

Probability distributions of thermodynamic affinities for heterogeneous receptor populations.

A statistical approach to characterize the thermodynamic affinity distributions of heterogeneous receptor populations in terms of stoichiometric binding constants is presented. The use of stoichiometric density distributions provides a novel description of ligand binding systems. The distributions of stoichiometric constants, Ti(Ki)'s, are obtained assuming that the distribution of site constants N(k) is known. It is found that in the case of heterogeneous systems with multivalent receptors, N(k) is an average over all the Ti(Ki)'s even when there are positive or negative site-site interactions. It is seen that in the absence or in the presence of site-site interactions the mean and the variance of the Ki's can be derived from a Scatchard plot. Some of these results are particularly applicable to bivalent heterogeneous antibody populations and other results are applicable to bivalent heterogeneous systems with different binding sites.

Antigen-Antibody Reactions↗
PubMed2000

A power analysis of microsatellite-based statistics for inferring past population growth.

We present results concerning the power to detect past population growth using three microsatellite-based statistics available in the current literature: (1) that based on between-locus variability, (2) that based on the shape of allele size distribution, and (3) that based on the imbalance between variance and heterozygosity at a locus. The analysis is based on the single-step stepwise mutation model. The power of the statistics is evaluated for constant, as well as variable, mutation rates across loci. The latter case is important, since it is a standard procedure to pool data collected at a number of loci, and mutation rates at microsatellite loci are known to be different. Our analysis indicates that the statistic based on the imbalance between allele size variance and heterozygosity at a locus has the highest power for detection of population growth, particularly when mutation rates vary across loci.

Evolution, Molecular↗
PubMed1989

A SAS procedure for exact probability testing of difference between sample and population proportion.

Statistical testing of the hypothesis that the proportion of subjects in a defined population having a certain attribute (proportion of "positives" in a population, P) is equal to some specified value (P0) is frequently encountered in biomedical research. For example, a study might be carried out to statistically test whether the postoperative wound infection rate in patients having undergone an operation with a "new" surgical procedure is 20%, the same value that has been observed for the "established" surgical procedure. The significance test for this hypothesis (e.g., test H0: P = 0.20 against HA: P not equal to 0.20) is usually based on the normal theory approximation method. However, when the sample size is "small", especially if P0 is close to 0 or 1, the normal theory method can yield grossly unreliable results. In contrast, the significance test based on the exact binomial probability procedure always yields reliable results. A computer program coded in SAS is described herein to perform this exact probability test procedure.

Mathematical Computing↗
PubMed2006

[Anthropometric patterns in non-Caucasian full-term neonates of African, Moroccan and South American origin born in Catalonia (Spain)].

INTRODUCTION: The rise in immigration to Spain in recent decades has increased the number of non-Caucasian newborns in our environment. The aims of this study were to establish normal intrauterine development values for weight, length and head circumference in a population of non-Caucasian full-term newborns (FTN). PATIENTS AND METHODS: We studied 2,444 healthy full-term singleton newborns (37-42 weeks' gestational age; 1,230 boys, 1,214 girls) with the following ethnic origins: black (n =1,257; 622 boys, 635 girls), Moroccan (n =520; 297 boys, 223 girls) and South-American (n =667; 356 boys, 311 girls). Mean values and standard deviations were estimated for each week of gestation for sex and race and these values were compared with those of a Spanish population of the same gestational age and sex. RESULTS: Anthropometric values in black FTN were similar to those of the Catalan population. By contrast, these values were higher in Moroccans and South-American FTN than in the native population. Statistically-significant differences were observed in all the parameters evaluated from the 38th week of gestation in full-term Moroccan newborns compared with the reference population. Statistically significant differences were observed in full-term South-American newborns from the 38th week of gestation in girls and from the 40th week in boys. The presence of sexual dimorphism in the anthropometric patterns evaluated was not constant at all the gestational ages evaluated. CONCLUSIONS: Anthropometric patterns of the Spanish Caucasian FTN population are not extrapolable to FTN of other ethnicities.

Africa↗