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Biomedical subjects

N R Mendell

Publications and source records attributed to N R Mendell.

At least 37 records · Page 2Linked to original sources
PubMed1991

Sex differences in high density lipoprotein cholesterol among low-level alcohol consumers.

The purpose of this study was to examine high density lipoprotein cholesterol (HDL-C) levels in a sample of community-living women and men who consumed 1 drink of alcohol/day or less. Self-reports of alcohol consumption and clinical assessments of plasma lipid and lipoprotein levels were obtained twice, at 12 months apart. Among men, consumption of 1 drink/day or less was unrelated to levels in HDL-C. In contrast, among women alcohol consumption throughout this relatively low consumption range was positively associated with HDL-C levels. These findings indicate that the association of alcohol and higher levels of HDL-C may occur at lower intakes of alcohol in women than in men.

Adult↗
PubMed1991

The likelihood ratio test for the two-component normal mixture problem: power and sample size analysis.

We find, through simulation and modeling, an approximation to the alternative distribution of the likelihood ratio test for two-component mixtures in which the components have different means but equal variances. We consider the range of mixing proportions from 0.5 through .95. Our simulation results indicate a dependence of power on the mixing proportion when pi less than .2 and pi greater than .80. Our model results indicated that the alternative distribution is approximately noncentral chi-square, possibly with 2 degrees of freedom. Using this model, we estimate a sample of 40 is needed to have 50% power to detect a difference between means equal to 3.0 for mixing proportions between .2 and .8. The sample size increases to 50 when the mixing proportion is .90 (or .1) and 82 when the mixing proportion is .95 (or .05). This paper contains a complete table of sample sizes needed for 50%, 80%, and 90% power.

Alleles↗
PubMed1988

Simulated percentage points for the null distribution of the likelihood ratio test for a mixture of two normals.

We find the percentage points of the likelihood ratio test of the null hypothesis that a sample of n observations is from a normal distribution with unknown mean and variance against the alternative that the sample is from a mixture of two distinct normal distributions, each with unknown mean and unknown (but equal) variance. The mixing proportion pi is also unknown under the alternative hypothesis. For 2,500 samples of sizes n = 15, 20, 25, 40, 50, 70, 75, 80, 100, 150, 250, 500, and 1,000, we calculated the likelihood ratio statistic, and from these values estimated the percentage points of the null distributions. Our algorithm for the calculation of the maximum likelihood estimates of the unknown parameters included precautions against convergence of the maximization algorithm to a local rather than global maximum. Investigations for convergence to an asymptotic distribution indicated that convergence was very slow and that stability was not apparent for samples as large as 1,000. Comparisons of the percentage points to the commonly assumed chi-squared distribution with 2 degrees of freedom indicated that this assumption is too liberal; i.e., one's P-value is greater than that indicated by chi 2(2). We conclude then that one would need what is usually an unfeasibly large sample size (n greater than 1,000) for the use of large-sample approximations to be justified.

Biometry↗
PubMed1986

Group participation and survival among patients with end-stage renal disease.

All 126 End-Stage Renal Disease (ESRD) patients who entered dialysis between 1971 and 1981 at the Harlem Hospital Center, New York City, were separated into those who had participated in a patient support group and those who had not done so. Patients who engaged in the group activities survived considerably longer than non-participants. Family history of renal disease, psychiatric illness, blood urea nitrogen (BUN), and creatinine were also related to survival, but, education, religion, marital status, and age were not. When 13 psychosocial and physiological covariates were controlled for in a Cox proportional hazard analysis, the group participation effect remained substantial.

Blood Urea Nitrogen↗
PubMed1983

Effect of population associations and reduced penetrance on observed and expected genotype frequencies in a simple genetic model: application to HLA and insulin dependent diabetes mellitus.

The observed and Hardy--Weinberg-expected frequencies for (HLA) marker heterozygotes in a disease population are calculated where it is assumed that the disease is caused by either homozygosity or heterozygosity (with reduced pentrance) for a disease susceptibility allele at a disease locus, that allele being positively associated with both of the relevant alleles at the marker locus (the single susceptibility allele model of Svejgaard & Ryder, 1981). It is shown that the observed frequency is always less than or equal to the H-W expectation, with the (observed/expected) ratio decreasing as the degree of dominance increases.

Alleles↗
PubMed1982

Ra3 skin test response and HLA-A2, antigen E, and IgE: evidence of interactions between antigen E and HLA.

A positive association of Ra3 skin test responses with HLA-A2 has previously been reported to be evident in individuals with low IgE levels and to a greater extent in these individuals than those with high IgE levels. We give evidence based on an analysis of data from 133 individuals that Ra3 response is positively correlated with HLA-A2 among individuals with low Antigen E response and negatively associated with HLA-A2 among individuals with high Antigen E response. Furthermore, we have evidence that any observed interaction between Ra3, IgE, and HLA-A2 can be explained by the correlation between IgE and Antigen E response, and that it is Antigen E response which interacts in the relationship between HLA-A2 and Ra3 skin test response.

Alleles↗
PubMed1981

Statistical methods for studying homozygous typing cells of unknown specificity.

A situation can arise in D typing in which the HLA (A,B,C,D, or DR) specificities of the responders are known and the specificities of the HTC's are unknown. The most powerful and direct method of detecting association between the unknown stimulator (HTC) and any given HLA specificity is by comparing the observed double normalized values (DNV's) of individuals known to be positive for the specificity with the DNV's of negative individuals. This can be done by comparing the two groups with a Kolmogorov-Smirnov test (K-S test), an established statistical procedure for evaluating correlation between continuous variables, such as the DNV, and discrete variables (such as presence of D type). The application of the K-S test will generate as a "cutoff" value of point that maximizes the average of the frequencies of correct assignments in D positives and D negatives. We also propose an alternative method of computing the "r" value. We have analyzed 49 HTC's from the 8th International Workshop and present the association observed with the D and DR specificities.

Alleles↗
PubMed1981

Familial predisposition to filarial infection--not linked to HLA-A or-B locus specificities.

Two hundred and twenty-five Polynesians were selected from a larger study population for the evaluation of potential genetic influences on the susceptibility to bancroftian filariasis. Analysis showed that there was significantly familial clustering of patients with filariasis and that this clustering was most compatible with genetic transmission of disease susceptibility. The data best fit a model in which the hypothetical gene for filariasis was recessive with a frequency of 0.82 +/- 0.15 in the population and a penetrance of 0.62 +/- 0.14. The alternative hypothesis that susceptibility was environmentally (i.e., not genetically) determined was also compatible with the data but was estimated to be 1.9 times less likely to account for the observed findings than the genetic hypothesis. Extensive evaluation of HLA-A and -B locus specificities failed to detect significant linkage either between particular antigen specificities and the clinical manifestations of filariasis or between individual haplotypes (indicated by HLA markers in studies of large families) and the predisposition to filarial infection or disease.

Adolescent↗
PubMed1978

Factors which have a significant effect on the survival of human skin grafts.

Survival of 436 ABO-compatible skin grafts exchanged in 97 Caucasian families was prolonged if donor and recipient were genotypically, as compared with phenotypically, HLA identical. Among skin grafts between haploidentical family members, a mismatch at the A locus was equivalent to a mismatch at the B locus. Skin grafted from child to mother survived longer than did skin grafted between other family members, other variables being equivalent. A highly significant positive correlation was found between the age of recipient and skin graft survival. In addition, a significant interaction was found between the relationship of donor and recipient and degree of antigen match.

Graft Survival↗
PubMed1978

Lack of linkage between hereditary angioedema and the A and B loci of the HLA system.

A large 81 member, four-generation black family with hereditary angioedema is reported with regards to its clinical course and the association with the histocompatibility system. No mortality was seen related directly to the disease. Assuming that this trait is autosomal dominant it appeared to have no linkage with the histocompatibility system as noted by an estimated recombination rate in males and females of 0.5 and a maximum lod score of 0.0. Further evidence of no linkage is given by the fact that lod scores below -3.0 were observed for values of theta less than 0.5.

Angioedema↗