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N Mantel

Publications and source records attributed to N Mantel.

At least 55 records · Page 3Linked to original sources
PubMed1985

Maximum likelihood vs. minimum chi-square.

In minimum chi-square logit or probit analysis of quantal bioassay data, a requirement for proper asymptotic behavior of the estimates made is that test-group sizes get indefinitely large. Inconsistent estimates result if group sizes are small, however numerous the groups. Maximum likelihood estimates do not show this inconsistent behavior, even if all the many group sizes are only unity. The inconsistent behavior for minimum chi-square results from a bias toward 0.5 for response probabilities. At 0.5 the binomial variance is at a maximum of 0.25, so tending to minimize the calculated value of chi square. The principle of minimum chi-square should not be confused with the principle of least squares.

Animals↗
PubMed1981

Are clinical trials in coronary heart disease oversold or undersold?

Randomized clinical trials constitute the formal experiments in therapeutics. Many such trials in coronary heart disease have terminated inconclusively or in controversy. In this editorial, we analyze some of the methodologic issues that may lead to controversy; the main reason for the low success rate may lie in insufficient understanding of the complex biology of the disease and in failure to select the appropriate models for therapy. We argue that these difficulties only strengthen the need for the rigorous experimental approach to the evaluation of therapies for coronary heart disease.

Aspirin↗
PubMed1980

Limited usefulness of mathematical models for assessing the carcinogenic risk of minute doses.

No mathematical model for carcinogenesis can cover all the exigencies of life. The usefulness of any model is consequently limited. A model may provide a basis for graduating data, though it need not be altogether valid to give reasonable graduations in the observable range and competing models could do as well. Or for providing useful insights into situations, a model need not be completely valid. But for the problematic issue of extrapolating to minute doses, the question of validity is crucial. A variety of related issues and approaches are discussed, beginning with a kinetic model proposed by Cornfield. Other discussions relate to the empirical relationship described by Druckrey, the linear model approach espoused by Crump and Guess and their associates, the safe dose estimation procedure of Hartley and Sielken and the relation of these approaches to the Mantel-Bryan approach. Issues like between-species extrapolation, limiting concern to near lifetime risks, occupational exposures vs. general population exposures are also considered.

Carcinogens↗
PubMed1980

Assessing laboratory evidence for neoplastic activity.

A variety of statistical issues which arise in the analysis of tumorigenesis assay data are reviewed. Tumor acceleration appeared as a possibility in the Red Dye 40 situation and that phenomenon is discussed. Experimental design considerations covered include sex, cage locations, and whether there is complete randomization, or whether littermates are stratified across doses, or whether, as in multigeneration studies, all littermates are treated alike. Whichever, the statistical analysis should be appropriate. Statistical techniques must take into account the time-to-response aspect in the detection of palpable tumors along with the complication of censored observation due to interim mortality. A logrank technique for accomplishing this must be further adjusted so as to handle tumors detectable only on necropsy. Dosage effects may be sought in a variety of ways, including alternative procedures for identifying progressive dosage effects. Separate analyses may be conducted for separate tumor sites or types, introducing a multiple-testing aspect. Because of the sparseness of data for many individual tumor sites, the usual multiple-testing procedures have to be modified. Statistical analysis, however, is only a guide to the careful interpretation of results, and the need to take action as a result of that interpretation remains.

Animals↗