Biomedical subjects

M Eliasziw

Publications and source records attributed to M Eliasziw.

9 recordsLinked to original sources

PubMed1992

A goodness-of-fit approach to inference procedures for the kappa statistic: confidence interval construction, significance-testing and sample size estimation.

We propose a new procedure for constructing a confidence interval about the kappa statistic in the case of two raters and a dichotomous outcome. The procedure is based on a chi-square goodness-of-fit test as applied to a model frequently used for clustered binary data. The procedure provides coverage levels that are accurate in samples of smaller size than those required for other procedures. The procedure also has use for significance-testing and the planning of corresponding sample size requirements.

Confidence Intervals↗

PubMed1991

Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis.

BACKGROUND: Without strong evidence of benefit, the use of carotid endarterectomy for prophylaxis against stroke rose dramatically until the mid-1980s, then declined. Our investigation sought to determine whether carotid endarterectomy reduces the risk of stroke among patients with a recent adverse cerebrovascular event and ipsilateral carotid stenosis. METHODS: We conducted a randomized trial at 50 clinical centers throughout the United States and Canada, in patients in two predetermined strata based on the severity of carotid stenosis--30 to 69 percent and 70 to 99 percent. We report here the results in the 659 patients in the latter stratum, who had had a hemispheric or retinal transient ischemic attack or a nondisabling stroke within the 120 days before entry and had stenosis of 70 to 99 percent in the symptomatic carotid artery. All patients received optimal medical care, including antiplatelet therapy. Those assigned to surgical treatment underwent carotid endarterectomy performed by neurosurgeons or vascular surgeons. All patients were examined by neurologists 1, 3, 6, 9, and 12 months after entry and then every 4 months. End points were assessed by blinded, independent case review. No patient was lost to follow-up. RESULTS: Life-table estimates of the cumulative risk of any ipsilateral stroke at two years were 26 percent in the 331 medical patients and 9 percent in the 328 surgical patients--an absolute risk reduction (+/- SE) 17 +/- 3.5 percent (P less than 0.001). For a major or fatal ipsilateral stroke, the corresponding estimates were 13.1 percent and 2.5 percent--an absolute risk reduction of 10.6 +/- 2.6 percent (P less than 0.001). Carotid endarterectomy was still found to be beneficial when all strokes and deaths were included in the analysis (P less than 0.001). CONCLUSIONS: Carotid endarterectomy is highly beneficial to patients with recent hemispheric and retinal transient ischemic attacks or nondisabling strokes and ipsilateral high-grade stenosis (70 to 99 percent) of the internal carotid artery.

Aged↗

PubMed1991

Application of the McNemar test to non-independent matched pair data.

McNemar's one degree of freedom chi-square test for the equality of proportions appears frequently in the analysis of pairs of matched, binary outcome data (Y1i, Y2i). An assumption underlying this test is that the responses from pair to pair are mutually independent. In certain applications, however, the pairs may represent repeated measurements on the same experimental unit, and hence this assumption is violated. In this paper we suggest an adjustment to the McNemar test to account for the repeated measures clustering effect and we report on a Monte Carlo simulation that evaluates the effectiveness of this approach.

Clinical Trials as Topic↗

PubMed1991

Methodology for inferences concerning familial correlations: a review.

There has been considerable methodologic research over the past 15 years on inference procedures for familial correlations. This paper reviews the various methods used to estimate sibling and parent-offspring correlations in family studies published over a recent 2-year period. The advantages and disadvantages of the various methodologic approaches are discussed, and practical recommendations given. One recommendation is for more frequent use of interval estimation. Computational formulas for selected approaches are presented in the appendices.

Analysis of Variance↗

PubMed1991

A generalized non-iterative approach to the analysis of family data.

A unified non-iterative approach to point and interval estimation of interclass and intraclass correlations is presented in the context of family studies where there may be more than one individual in each of two classes. The procedure involves a generalization of the Pearson product-moment correlation coefficient, where one permits different weights for the pairs of scores. Unlike the maximum likelihood approach, these estimators are not derived under the assumption of a particular parametric form nor do they require an iterative solution. The asymptotic distributions of the generalized product-moment estimator and of the maximum likelihood estimator are derived under the assumption of normality. Also, several methods for constructing confidence intervals about the interclass correlation parameter are outlined, and the effectiveness of these methods is evaluated by Monte Carlo simulation. Although the focus of this paper is on the analysis of familial data, the methods discussed are applicable to more general situations, including the assessment of correlations between any two variables where each variable is replicated a different number of times for each sample unit.

Analysis of Variance↗

PubMed1991

Application of matched pair procedures to site-specific data in periodontal research.

Application of standard statistical procedures to site-specific data in periodontal research is invalid unless site-to-site dependencies are accounted for. In this paper, we present the adjustments required for valid application of matched pair procedures, including the paired t-test and McNemar's chi 2 test for correlated proportions. Examples are given involving data arising from: (1) the comparison of pre- and post-treatment clinical measurements; (ii) split-mouth protocols.

Chlorhexidine↗

PubMed1990

Comparison of recent estimators of interclass correlation from familial data.

The asymptotic and finite-sample properties of several recent estimators of interclass correlation are compared to more traditional estimators in the case of a variable number of siblings per family. It is shown that Karlin's family-weighted pairwise estimator (Karlin, Cameron, and Williams, 1981, Proceedings of the National Academy of Science 78, 2664-2668) is virtually equivalent to the ensemble estimator (Rosner, Donner, and Hennekens, 1977, Applied Statistics 26, 179-187), thus suggesting an estimator of the former's asymptotic variance. Further, an estimator proposed by Srivastava (1984, Biometrika 71, 177-185) is shown to be identical to the modified sib-mean estimator (Konishi, 1982, Annals of the Institute of Statistical Mathematics 34, 505-515) when the sib-sib correlation is estimated by the method of unweighted group means. Although the estimator due to Srivastava has smaller asymptotic variance than the other two, the gain in efficiency is slight, for familial data, both asymptotically and in finite samples.

Analysis of Variance↗

PubMed1987

Sample size requirements for reliability studies.

This paper provides exact power contours to guide the planning of reliability studies, where the parameter of interest is the coefficient of intraclass correlation rho derived from a one-way analysis of variance model. The contours display the required numbers of subjects k and number of repeated measurements n that provide 80 per cent power for testing Ho: rho less than or equal to rho 0 versus H1: rho greater than rho 0 at the 5 per cent level of significance for selected values of rho o. We discuss the design considerations of these results.

Analysis of Variance↗

PubMed1987

A cost-function approach to the design of reliability studies.

We present a method to determine the number of subjects, k, and number of repeated measurements, n, that minimize the overall cost of conducting a reliability study, while providing acceptable power for tests of hypotheses concerning the reliability coefficient rho. Tables showing optimal choices of k and n under various cost constraints also appear. We discuss design considerations for reliability studies in light of the results.

Analysis of Variance↗