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Biomedical subjects

J Cornfield

Publications and source records attributed to J Cornfield.

7 recordsLinked to original sources
PubMed1979

Selection on atherosclerosis as an explanation of the attenuated cholesterol-mortality relation in coronary heart disease populations.

Recent studies of patients with coronary heart disease (CHD) at baseline have shown that their cholesterol levels are much less predictive of subsequent mortality than in populations free of CHD (FCHD). One previously suggested explanation of this attenuation is that the impact of hyperlipidemia on atherosclerosis or of atherosclerosis on mortality is reduced for post-myocardial infarction patients. In this paper it is shown that an alternative explanation is selection of CHD populations from FCHD populations for higher atherosclerosis levels. Data from all known follow-up studies on patients with baseline coronary angiograms are assembled to yield relations between cholesterol, atherosclerosis and mortality in CHD and FCHD populations. These data show that the selection hypothesis is not only logically possible but is also consistent with presently available epidemiologic information on relations between these three variables. An ethically impracticable large prospective study of a FCHD population with baseline angiograms might, however, be needed to choose definitively between the selection and reduced impact hypotheses.

Arteriosclerosis↗
PubMed1977

Carcinogenic risk assessment.

Carcinogenic risk assessment involves a mixture of statistical, scientific, and public policy considerations. Concepts in current use, such as "no observed effect levels" and "virtual safety," and the problems in implementing them by means of dose-response models, particularly the probit-log dose and linear models are reviewed. The upper limits to risk provided by some conservative procedures are inconsistent with coherent balancing of risks and benefits. A common basis to the dose-response curves describing both carcinogenic and noncarcinogenic effects is to be found in deactivating reactions. A simplified model in which a toxic substance is activated and deactivated in separate and simultaneous reactions is presented and the dose response curve implied by the model is deduced. This curve has the general form of a hockey stick, with the striking part flat or nearly flat until the dose administered saturates the deactivation system, after which the probability of a response rises rapidly. Such a curve describes the Bryan-Shimkin methylcholanthrene-tumor incidence dose response curve as well as the probit log-dose model. The concept of a saturation dose is relevant to risk assessments for carcinogenic and noncarcinogenic substances alike.

Carcinogens↗
PubMed1975

Clinical application of a second generation electrocardiographic computer program.

An electrocardiographic computer program based on multivariate analysis of orthogonal leads (Frank) was applied to records transmitted daily by telephone from the Veterans Administration Hospital, West Roxbury, Mass., to the Veterans Administration Hospital, Washington, D. C. A Bayesian classification procedure was used to compute probabilities for all diagnostic categories that might be encountered in a given record. Computer results were compared with interpretations of conventional 12 lead tracings. Of 1,663 records transmitted, 1,192 were selected for the study because the clinical diagnosis in these cases could be firmly established on the basis of independent, nonelectrocardiographic information. Twenty-one percent of the records were obtained from patients without evidence of cardiac disease and 79 percent from patients with various cardiovascular illnesses. Diagnostic electrocardiographic classifications were considered correct when in agreement with documented clinical diagnoses. Of the total sample of 1,192 recordings, 86 percent were classified correctly by computer as compared with 68 percent by conventional 12 lead electrocardiographic analysis. Improvement in diagnostic recognition by computer was most striking in patients with hypertensive cardiovascular disease or chronic obstructive lung disease. The multivariate classification scheme functioned most efficiently when a problem-oriented approach to diagnosis was simulated. This was accomplished by a simple method of adjusting prior probabilities according to the diagnostic problem under consideration.

Analysis of Variance↗
PubMed1975

The program of the cooperative study of the Veterans Administration.

A computer program for the automatic analysis of the electrocardiogram is described with details about wave recognition, measurements, and the calculation of the posterior probabilities of each diagnosis. The advantages and disadvantages of this multivariate statistical procedure are discussed. Classification statements result from separate analysis of the QRS-T complex, P wave, and ST segment. Criteria for inclusion of the patients forming the data base are given, with tables of measurements, means and standard deviation, as well as investigation of agreement between calculated and observed probabilities. Estimated error rates are given in the form of misclassification matrices, computed from large numbers of tracings collected by a Veteran Administration Cooperative Study, where the correct diagnoses are taken from clinical, laboratory, and autopsy information.

Cardiomegaly↗