PubMed Health⌕ Search

Biomedical subjects

R DerSimonian

Publications and source records attributed to R DerSimonian.

13 recordsLinked to original sources
PubMed1996

Meta-analysis in the design and monitoring of clinical trials.

Results from external studies often play an important role in many aspects of a clinical trial. Their incorporation into the decision making process of a trial, however, is rarely conducted in a formal manner. This conference will address what formal role, if any, meta-analytic summaries of external results should have in the design and monitoring of an ongoing trial. This introductory presentation describes in detail the example from obstetric research which motivated the conference topic, and, in a Bayesian framework, summarizes the general implications of formally incorporating meta-analytic results into the design and analysis of a new trial.

Bayes Theorem↗
PubMed1996

Trial of Calcium for Preeclampsia Prevention (CPEP): rationale, design, and methods.

The results of ten clinical trials suggest that supplemental calcium may prevent preeclampsia. However, methodologic problems and differences in study design limit the acceptance of the results and their relevance to other patient populations. Many of the trials were conducted in countries where, unlike the United States, the usual daily diet contained little calcium. Moreover, none of the trials has reported the outcome of systematic surveillance for urolithiasis, a potential complication of calcium supplementation. In response to the need for a thorough evaluation of the effects of calcium supplementation for the prevention of preeclampsia in the United States, the trial of Calcium for Preeclampsia Prevention (CPEP) was undertaken at five university medical centers. Healthy nulliparous patients were randomly assigned to receive either 2 g supplemental calcium daily (n = 2295) or placebo (n = 2294) in a double-blind study. Study tablets were administered beginning from 13 to 21 completed weeks of gestation and continued until the termination of pregnancy. CPEP employed detailed diagnostic criteria, standardized techniques of measurement, and systematic surveillance for the major study endpoints and for urolithiasis. The nutrient intake of each patient was assessed at randomization and at 32-33 weeks gestation. This report describes the study rationale, design, and methods.

Calcium↗
PubMed1993

Vasectomy and prostate cancer risk: methodological review of the evidence.

Two recent studies have reported a significantly elevated risk of prostate cancer among vasectomized men. To assess whether the new results conflict with earlier studies that found no significant overall association, and, if so, whether such a conflict could have a methodological basis, we reviewed the six major epidemiological studies of this topic. Statistical analysis revealed significant (p < 0.01) heterogeneity among the associations in the six studies, attributable to one of the recent studies. Scrutiny of the studies for fulfillment of eight methodological standards for scientific validity revealed that no study completely fulfilled more than four standards, and that all studies were deficient in avoiding detection bias and obtaining accurate vasectomy histories. Our review indicates that the evidence on this topic is indeed conflicting, that the quality of the evidence does not resolve the conflict, and that future studies of this topic, designed to ensure scientific credibility of results, are needed.

Adult↗
PubMed1992

An analysis of interobserver recognition of the histopathologic features of dysplastic nevi from a mixed group of nevomelanocytic lesions.

BACKGROUND: The diagnostic criteria for the histopathologic recognition of the dysplastic nevus are defined, but difficult to apply in practice. However, the use of skin biopsy is on the increase to search for this nevus because of a possible role in melanomagenesis. OBJECTIVE: The aim was to determine the degree of observer reproducibility in the detection of histologic nevomelanocytic dysplasia as measured across multiple observers and to test whether each observer was precise over a wide sample population. A second aim was to gain some measure of the threshold a person has for such lesions. METHODS: Histologic specimens from 50 coded nevomelanocytic tumors, which included a group of dysplastic nevi, were independently read by five observers in a blinded fashion. At study completion, the same 50 cases were read again by a melanoma reference pathologist and results analyzed by Cohen's kappa to assess agreement and interobserver variation. RESULTS: Corrected rates of agreement for dysplastic nevi ranged from 0.32 to 0.71. CONCLUSION: Continued study and experience are required for precision and reproducibility in the histologic recognition of dysplastic nevi.

Dysplastic Nevus Syndrome↗
PubMed1992

Interpretation of linear regression models that include transformations or interaction terms.

In linear regression analyses, we must often transform the dependent variable to meet the statistical assumptions of normality, variance stability, or linearity. Transformations, however, can complicate the interpretation of results because they change the scale on which the dependent variable is measured. In this setting, the inclusion of product terms or the transformation of some independent (or predictor) variables may further complicate interpretation. In this article, we present some interpretations of linear models that include transformations or product terms. We illustrate these interpretations using regression analyses designed to study determinants of serum testosterone levels. These examples show how one can present results using simple measures, such as medians, and interpret regression parameters.

Epidemiologic Methods↗
PubMed1990

Changes in Connecticut hospital use rates: have small-area variations been affected?

This paper examines the extent to which changes (prospective payment, alternative delivery systems, etc.) in the hospital environment and the general decline in hospital days affect small-area variations in hospital use rates for 18 selected diagnoses in nine hospital service areas in Connecticut. After adjusting for coding changes between DRGs, we found that variation across the service areas did not, in general, differ for any one of the years 1981-86. In one instance (cardiac catheterization), however, we found that a DRG-specific change in knowledge and technology decreased the extent of small-area variation for that diagnosis.

Analysis of Variance↗
PubMed1986

Meta-analysis in clinical trials.

This paper examines eight published reviews each reporting results from several related trials. Each review pools the results from the relevant trials in order to evaluate the efficacy of a certain treatment for a specified medical condition. These reviews lack consistent assessment of homogeneity of treatment effect before pooling. We discuss a random effects approach to combining evidence from a series of experiments comparing two treatments. This approach incorporates the heterogeneity of effects in the analysis of the overall treatment efficacy. The model can be extended to include relevant covariates which would reduce the heterogeneity and allow for more specific therapeutic recommendations. We suggest a simple noniterative procedure for characterizing the distribution of treatment effects in a series of studies.

Clinical Trials as Topic↗
PubMed1986

Prognostic role of antibody reactivity to melanoma.

Antibody reactivity against cultured allogeneic melanoma Y-Mel 81:180 was studied in 43 patients who participated in an adjuvant trial for stage I and II melanoma. Serum samples were obtained at trial entry within 2 mo of definitive surgery. At the time of serum acquisition, all patients were free of disease by physical examination and routine radiologic and laboratory parameters. Serum antibody reactivity was tested for by protein A hemadsorption before and after acid dissociation and ultrafiltration of serum. We have previously shown that this technique for immune complex dissociation augments autologous antibody reactivity. Results of serum antibody reactivity were scored by an investigator blinded to the patient's clinical status. Of the 43 patients studied, 15 relapsed and 28 remained disease-free. At study entry, there were 25 stage I patients and 18 stage II patients. Breslow depth was 3.25 +/- 2.5 mm in relapse patients and 1.67 +/- 1.1 mm in disease-free patients. The presence and titer of antibody directed against melanoma in either native serum or serum dissociated from immune complexes was found to be associated with eventual relapse (P = 0.0001). When results were subgrouped by stage of disease, Breslow depth, and hypopigmentation, antibody reactivity was still correlated with eventual relapse. The incidence and titer of antibody reactivity against melanoma appears to be a new prognostic factor in predicting eventual disease recurrence.

Adult↗
PubMed1982

Reporting on methods in clinical trials.

A clinical trial cannot be adequately interpreted without information about the methods used in the design of the study and the analysis of the results. To determine the frequency of reporting what we consider 11 important aspects of design and analysis, we surveyed all 67 clinical trials published in the New England Journal of Medicine, the Lancet, and the British Medical Journal from July through December 1979 and in the Journal of the American Medical Association from July 1979 through June 1980. Of all 11 items in the 67 trials published in all four journals, 56 per cent were clearly reported, 10 per cent were ambiguously mentioned, and 34 per cent were not reported at all. At least 80 per cent of the 67 trials reported information about statistical analyses, statistical methods used, and random allocation of subjects, yet only 19 per cent reported the method of randomization. Loss to follow-up was discussed in 79 per cent of the articles, treatment complications in 64 per cent, and admission of subjects before allocation in 57 per cent, but eligibility criteria for admission to the trial appeared in only 37 per cent. Although information about whether patients were blind to treatment was given in 55 per cent, information about whether there was blind assessment of outcome was reported in only 30 per cent. The statistical power of the trial to detect treatment effects was discussed in only 12 per cent of the articles. The clinical trials published in The New England Journal of Medicine reported 71 per cent of the 11 items, those in the Journal of the American Medical Association 63 per cent, those in the British Medical Journal 52 per cent, and those in the Lancet 46 per cent. These rates are significantly different (P less than 0.001). We recommend that editors improve the reporting of clinical trials by giving authors a list of the important items to be reported.

Biometry↗