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Biomedical subjects

A Donner

Publications and source records attributed to A Donner.

At least 127 records · Page 7Linked to original sources
PubMed1988

The statistical analysis of multiple binary measurements.

Epidemiologic studies often compare several groups of subjects for the presence or absence of a specified biological trait, where each subject in a group contributes two or more observations to the analysis. Examples occur in ophthalmologic studies, where each subject contributes observations on each of two eyes, and dental studies, where observations on each of several teeth may be contributed. Application of the standard Pearson chi-square test to such data is not valid, since the resulting sample observations are not statistically independent. In this paper we show how simple adjustments can be made to the Pearson chi-square statistic that adjust for the within-subject clustering. Application to other types of investigations involving clustered data is also discussed.

Adult↗
PubMed1988

The effects of kaolin on the lung.

We studied the prevalence of ventilatory impairment, chest symptoms, and radiographic abnormality in a selected sample of more than 2,000 kaolin workers from east central Georgia. The presence of ventilatory impairment was related to the presence of complicated pneumoconiosis, employment in clay calcining, and cigarette smoking. In those working with calcined clay, there was an increased prevalence of abnormality of the FEV1, but not the FVC, when compared to both wet and dry processors and which could not be explained by either cigarette smoking or the presence of pneumoconiosis. The magnitude of abnormality in the calcined clay workers was, however, unlikely to lead to disabling impairment. In workers with more than 3-yr tenure, there were 90 subjects with simple pneumoconiosis and 18 with complicated pneumoconiosis, yielding an adjusted prevalence of 3.2% and 0.63%, respectively, in the sample examined. Dry processing was associated with a greater risk of developing pneumoconiosis than wet processing.

Adult↗
PubMed1988

Analysis of site-specific data in dental studies.

Much attention has been given recently to issues in the statistical analysis of site data arising from clinical trials in periodontics. As pointed out by Imrey (1986) and Fleiss et al. (1987), it is unreasonable to expect sites within the same patient to respond independently, and thus conventional statistical methods are not directly applicable. In this paper we develop a procedure for comparing the percentage of sites showing a given characteristic across two or more groups of patients that accounts for this lack of independence. The procedure is a straightforward extension of the standard Pearson chi-square test. Two examples are given.

Data Interpretation, Statistical↗
PubMed1988

Estimation of a common odds ratio in case-control studies of familial aggregation.

A new estimator of a common odds ratio is proposed for case-control studies of familial aggregation. The proposed estimator is a modification to the usual Mantel-Haenszel estimator that relies on an empirical adjustment for the within-family clustering which is typical of such designs. A simulation study shows that the estimator tends to have smaller mean squared error than the unmodified Mantel-Haenszel estimator under conditions likely to arise in practice. The construction of confidence intervals is also discussed.

Biometry↗
PubMed1988

Is population mobility an obstacle to continuity of care? Attrition rates over five years in 17 Ontario practices.

The University of Western Ontario Hypertension Study provided an opportunity to study attrition rates over a five-year period in the population of 17 family practices in southwestern Ontario. The baseline population consisted of all patients between the ages of 20 and 65 years who were active in the practices in 1978. During the five years of the study, a medical assistant in each practice recorded data on morbidity, mortality, and patients leaving the practice. The follow-up of nonresponders to a demographic questionnaire provided additional data on patient moves. The overall five-year move rate was 13.2 percent for men and 16.6 percent for women. Those in the 20- to 29-year age group had the highest rates, and those in the 30- to 39-year age group had the next highest. The rates for men stabilized after the age of 40 years to between 8 and 10 percent, and for women after 40 years to between 11 and 13 percent. The move rates were higher in urban than in rural practices. Ninety percent of hypertensive patients received continuous care over the five-year period. In southwestern Ontario, population mobility does not appear to be a major barrier to continuing care.

Adult↗
PubMed1987

[Specific therapy of acute benzodiazepine poisoning using flumazenil (Ro 15-1788)].

In 20 patients with coma (grade 4: n = 7, grade 3: n = 8, grade 2: n = 2, grade 1: n = 3) due to benzodiazepine intoxication, solely or combined with alcohol or other psychoactive drugs, the effect of a specific benzodiazepine antagonist, Flumazenil (Ro 15-1788), was evaluated. In terms of coma depth, 80% of the patients responded to application of 1.96 mg Flumazenil as a mean with immediate awakening or improvement of at least two steps in coma grading. In those 3 patients, who failed to respond to Flumazenil, the history revealed amitriptyline or barbiturates to be responsible for the comatose state. The observed side-effects of Flumazenil included increase (n = 4) or decrease (n = 3) of blood pressure, increase of heart rate (n = 7), cutaneous flush (n = 1) and ventricular extrasystoles (n = 1). Agitation and generalized convulsions, each observed in 1 patient, presumably were due to an acute benzodiazepine-withdrawal rather than an intrinsic side effect of the antagonist. In conclusion, Flumazenil proved to be a potent antagonist of benzodiazepines in patients with severe coma and even may serve as a valuable diagnostic in cases of suspected benzodiazepine intoxication.

Adult↗
PubMed1987

Cancer incidence in hypertensives.

Cancer incidence was measured over a 5-year period (1978 to 1982) in 4067 hypertensive patients, and 10,366 normotensive patients from general practices in southwestern Ontario. For cancer of all sites an elevated incidence was found among hypertensive patients. The elevation was most pronounced among newly diagnosed hypertensive patients, with hypertension of moderate or greater severity, and for sites that have been described in clinical reports as being capable of producing a rise in blood pressure. It is tentatively concluded that the causal direction is from cancer to hypertension, rather than the reverse. If this conclusion is correct, the associations that have been reported between cancer mortality and hypertension may be due to an effect of blood pressure upon survival from cancer.

Adult↗
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

Adjustments to the Mantel-Haenszel chi-square statistic and odds ratio variance estimator when the data are clustered.

Dependence between observations on a dichotomous variable renders invalid the usual chi-square tests of independence and inflates the variances of parameter estimates. Such a situation occurs, for example, when subjects consist of members of the same family or with repeated observations on the same person. In this paper we describe methods of measuring the extent of correlation (or clustering). We also develop methods of adjusting the Mantel-Haenszel chi-square test statistic and the variance of the Mantel-Haenszel estimate of a common odds ratio in sets of 2 X 2 contingency tables.

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↗
PubMed1987

Lack of impact of salt restriction advice on hypertensive patients.

The response of known hypertensives to advice on sodium restriction was examined as part of a 5-year study on hypertension screening in family practice. The study comprised 34 family practices, pair-matched for location, activity level, and length of time in present practice. One practice in each matched pair was randomly allocated to an experimental or a control group. All hypertensive patients in each experimental practice were exposed to a management program which included dietary counseling to restrict sodium intake. A sample of hypertensive patients (N = 1,001) in both control and experimental groups was interviewed 3.5 years into the study. Although more subjects in experimental practices reported not adding salt (22.9%) compared with those in control practices (17.3%), the results of multivariate analysis showed that type of practice (experimental or control) was not significantly associated with salt use. Salt avoidance was strongly related to lower levels of education and to sex (men were less likely to use salt). Subjects who did not use salt also tended to avoid high-sodium foods. The response to nutritional advice was less favorable than expected. Difficulties in compliance with dietary recommendations are discussed.

Adult↗
PubMed1987

Statistical methodology for paired cluster designs.

Recently developed methodology is applied to the analysis of data arising from a design in which an experimental intervention is assigned at random to one of two clusters in a matched pair. Standard statistical techniques do not apply to such data, since they do not take into account variation arising from differences among clusters as well as within clusters. The methodology presented provides a significance test over kappa pairs of clusters with respect to a dichotomous outcome variable while controlling for confounding. The investigation of interaction effects is also discussed.

Female↗
PubMed1987

The prognosis of hypertension according to age at onset.

Data from a program for hypertension screening and follow-up were used to study the relationship between age at onset of hypertension and the risk of cardiovascular complications. The risk for hypertensive subjects, compared with normotensive subjects of similar age, declined significantly as age of onset increased from 40 to 69 years. This pattern was not explained by differences in initial severity of hypertension, control of hypertension, obesity, smoking, or alcohol consumption. A sex-specific analysis showed that the pattern was confined to male subjects, but it is argued that it might be seen in female subjects if data for women of more advanced age were available. Further lines of investigation of this interesting phenomenon are proposed.

Adult↗