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Biomedical subjects

A Donner

Publications and source records attributed to A Donner.

At least 145 records · Page 8Linked to original sources

Do family physicians need medical assistants to detect and manage hypertension?

To test a new approach to detecting and managing hypertension, 34 family practices in southwestern Ontario that comprised 32 124 patients aged 20 to 65 years were randomly assigned in a 5-year study to either undertake a system of care in which a medical assistant oversaw screening and attended to education, compliance and follow-up (experimental group) or continue their usual practices (control group). The 17 physicians in the experimental practices (15 659 patients) were matched with the 17 in the control practices (16 465 patients) according to size of the community, sex, level of practice activity and length of time in practice. Hypertension was defined as at least two diastolic blood pressure readings over 90 mm Hg. More patients in the experimental group than in the control group were screened at least once (91% v. 80%); the former were more likely to have lower systolic blood pressure (p less than 0.02), to be compliant (p less than 0.05) and to be very satisfied with care (p less than 0.01). There were no significant differences between the two groups in the rates of illness and death due to cardiovascular disease for all patients or for hypertensive patients. The unassisted family physician can provide effective care for hypertensive patients. However, minor modifications in the physician's practices can improve care.

Adult↗

The large-sample relative efficiency of the Mantel-Haenszel estimator in the fixed-strata case.

The large-sample relative efficiency of the Mantel-Haenszel estimator psi MH of an odds ratio is investigated for the case in which the number of strata is fixed and the sample sizes within each stratum increase indefinitely. The results show that psi MH is very efficient over a wide range of designs likely to occur in practice. However, conditions are identified under which the relative efficiency of this widely used estimator can be unusually low.

Analysis of Variance↗

A comparison of confidence interval methods for the intraclass correlation coefficient.

Different methods of obtaining confidence intervals for the intraclass correlation coefficient rho in the unbalanced one-way random-effects model are investigated, focusing on applications to family studies. Methods based on simple modifications of formulas for the case of equal group sizes are found to provide adequate coverage at small to moderate values of rho. A method based on the large-sample standard error of the sample intraclass correlation, as derived by Smith (1956, Annals of Human Genetics 21, 363-373), is shown to provide consistently good coverage at all values of rho. A method proposed by Thomas and Hultquist (1978, Annals of Statistics 6, 582-587) also provides consistently good coverage, but generates mean interval widths substantially greater than those generated by Smith's method at values of rho likely to arise in practice.

Biometry↗

A regression approach to the analysis of data arising from cluster randomization.

A generalized least squares regression approach is proposed for the analysis of data arising from experimental studies involving cluster randomization and non-experimental studies in which the major treatment factor corresponds to a characteristic which applies at the cluster level. This approach is more flexible than that provided by the analysis of variance, and unlike ordinary least squares, provides significance levels which are adjusted for the correlation among elements within the same cluster. Two examples are presented.

Adult↗

Behavior pattern A and compliance with antihypertensive treatment.

An analysis was performed on cross-sectional data on 512 hypertensive patients to look at the association of behavior pattern A (coronary prone behavior) and compliance with therapy. In a home interview behavior pattern A was assessed by a questionnaire (The Bortner scale), compliance by a vignette, and blood pressure was measured. Noncompliers showed a higher degree of Type A characteristics, that is there was a significant negative association between behavior pattern A and compliance (p = 0.02). It is proposed that a new variable, behavior pattern A, should be considered in future research on compliance.

Adult↗

The analysis of intraclass correlation in multiple samples.

A unified methodology is presented for the analysis of intraclass correlation in two or more samples, with emphasis on application to family studies. The methodology provides point and interval estimates of a common intraclass correlation in data having either fixed or variable class sizes. Tests of homogeneity for intraclass correlation coefficients are also discussed.

Genetics, Medical↗

Linear regression analysis with repeated measurements.

The statistical aspects of repeated measures linear regression, in which each subject contributes several pairs of measurements to the analysis, are discussed. It is shown that the standard error of a regression coefficient computed from the ordinary least squares analysis can either underestimate or overestimate the true standard error, depending on how values of the independent variable are selected. The application of generalized least squares analysis to repeated measures data is also discussed. Two examples are given.

Adolescent↗

A comparison of plans for hypertension screening.

Correcting to the work by Donner and Bull [1], it is reported that, in the setting they considered, screening plans based on the mean have higher power (probability of identifying a true hypertensive) than screening plans based on the minimum. However, for any reasonable size (probability of a false diagnosis of hypertension) the powers of the two plans are close.

Blood Pressure Determination↗

Acute oral poisoning with lindane-solvent mixtures.

Six cases of oral intoxication with lindane-solvent mixtures are reviewed. The ingested doses of lindane (mean dosage 120 mg/kg +/- 86 mg/kg) and benzene (mean dosage 366 mg/kg +/- 93 mg/kg) exceeded the toxic level. Symptoms (vomiting, dizziness and hyperreflexia) occurred within 30 min and all patients had epileptiform seizures. Two patients suffered from pulmonary edema and one of them had a severe rhabdomyolysis. Diazepam was sufficient to control convulsions in five cases. Gastric lavage was performed in five patients and activated charcoal, liquid paraffin with saline cathartic, and cholestyramine were used as adsorbents. Recovery was complete in all patients.

Administration, Oral↗

Testing the effect of sex differences on sib-sib correlations.

Procedures for testing the effect of sex differences on sib-sib correlations are studied. It is demonstrated that a simple procedure for testing the equality of a pair of brother-brother and sister-sister correlations (the modified Z test) is comparable in power to the likelihood ratio test in moderately large samples drawn from sibship-size distributions that are likely to occur in practice. In small samples, the modified Z test is preferable to the likelihood ratio test, since the latter tends to be anti-conservative.

Biometry↗

Regression analysis in physiological research: some comments on the problem of repeated measurements.

The statistical implications of repeated-measures linear regression, in which each subject contributes several pairs of measurements to the analysis, are discussed in the context of physiological research. The major point of the paper is that standard least-squares procedures cannot be applied without modification to regression problems with repeated measures. An example is given.

Adult↗

Antibodies to Epstein-Barr virus in nasopharyngeal carcinoma, tonsillar carcinoma and control groups.

In the sera of 17 patients with nasopharyngeal carcinoma (NPC) and of 19 patients with tonsillar carcinoma (TC) the titres of IgA, IgG and IgM antibodies to EBV VCA (viral capsid antigen) and of IgG antibodies to EBV EA (early antigen) were determined by the indirect immunofluorescence (IF) method. Significant difference was observed in the frequency of IgA antibodies to EBV VCA and IgG antibodies to EBV EA between NPC patients and controls. There was also a significant difference between the frequency of IgM antibody to EBV VCA and EBV EA antibody titres in TC patients and controls. The geometric mean titre (GMT) of IgG antibodies to EBV VCA was significantly higher in the NPC and TC patients as compared to controls.

Adult↗

Variance-component estimation from human sibship data.

The large-sample relative efficiencies of the analysis-of-variance (ANOVA) estimators of variance components and the intraclass correlation coefficient rho are investigated for the unbalanced single classification in the context of family studies. The efficiency of an analysis based on the method of unweighted group means is also investigated. From a Monte Carlo study which generates the group sizes from typical family-size distributions it is found that the relative efficiency of the ANOVA estimators of the between-group variance component exceeds 95% for values of .2 less than or equal to rho less than or equal to .4, but can fall below 60% for values of rho that are very close to zero. For the estimation of the between-group variance component the method of unweighted means tends to be preferable to the ANOVA method only if rho greater than .5.

Analysis of Variance↗

Inferences concerning a common intraclass correlation coefficient.

The maximum likelihood estimator, rhoM, of a common intraclass correlation, rho, is derived in two independent samples drawn from multivariate normal populations. A likelihood ratio statistic for testing the assumption of a common rho is also derived and examples are given. Comparisons are made with a procedure based on Fisher's transformation.

Models, Theoretical↗

A Bayesian approach to the interpretation of subgroup results in clinical trials.

Problems of interpretation often arise when patients who have been entered into a randomized clinical trial are post-stratified according to prognostic descriptors, and treatment comparisons performed within subgroups. In this paper a Bayesian approach to interpreting these comparisons is proposed, which takes into account the investigator's prior expectations concerning the relative magnitudes of treatment effects in different subgroups.

Bayes Theorem↗