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Biomedical subjects

T C Chalmers

Publications and source records attributed to T C Chalmers.

At least 19 recordsLinked to original sources
PubMed1992

Cumulative meta-analysis of therapeutic trials for myocardial infarction.

BACKGROUND: The large volume of published randomized, controlled trials has led to a need for meta-analyses to track therapeutic advances. Performing a new meta-analysis whenever the results of a new trial of a particular therapy are published permits the study of trends in efficacy and makes it possible to determine when a new treatment appears to be significantly effective or deleterious. We describe the use of such a procedure, cumulative meta-analysis, to assess therapeutic trials among patients with myocardial infarction. METHODS: We performed cumulative meta-analyses of clinical trials that evaluated 15 treatments and preventive measures for acute myocardial infarction. RESULTS: An example of this method is its application to the use of intravenous streptokinase as thrombolytic therapy for acute infarction. Thirty-three trials evaluating this therapy were performed between 1959 and 1988. We found that a consistent, statistically significant reduction in total mortality (odds ratios, 0.74; 95 percent confidence interval, 0.59 to 0.92) was achieved in 1973, after only eight trials involving 2432 patients had been completed. The results of the 25 subsequent trials, which enrolled an additional 34,542 patients through 1988, had little or no effect on the odds ratio establishing efficacy, but simply narrowed the 95 percent confidence interval. In particular, two very large trials, the Gruppo Italiano per lo Studio della Streptochinasi nell'Infarto Miocardico trial in 1986 (11,712 patients) and the Second International Study of Infarct Survival trial in 1988 (17,187 patients) did not modify the already established evidence of efficacy. We used a similar approach to study the accumulating evidence of efficacy (or lack of efficacy) of 14 other therapies and preventive measures for myocardial infarction. CONCLUSIONS: Cumulative meta-analysis of therapeutic trials facilitates the determination of clinical efficacy and harm and may be helpful in tracking trials, planning future trials, and making clinical recommendations for therapy.

Confidence Intervals↗
PubMed1992

A clinical trials database as a research tool in health care.

OBJECTIVE: The rapid, efficient, and accurate communication of clinical research findings to both clinicians and researchers is essential to the process of improving medical care. This information should be conveyed in a form that facilitates the interpretation of the complete body of research on a specific condition. Unfortunately, the prevailing system for dissemination of clinical research fails to meet these criteria. This paper proposes a system for cataloging clinical trials and communicating their results in a comprehensive and comprehensible format. METHOD: The system involves the use of a hierarchical matrix structure that allows for the selection and evaluation of related groups of clinical trials. The format of the data is tailored to the requirements of metaanalysis. RESULTS: An example is presented using the treatment of acute Crohn's disease and including a sample metaanalysis of immunosuppressive therapy for this condition. CONCLUSIONS: The hierarchical matrix structure in conjunction with a comprehensive database of clinical trials holds the potential to facilitate access to and interpretation of clinical research.

Acute Disease↗
PubMed1992

A comparison of results of meta-analyses of randomized control trials and recommendations of clinical experts. Treatments for myocardial infarction.

OBJECTIVE: To examine the temporal relationship between accumulating data from randomized control trials of treatments for myocardial infarction and the recommendations of clinical experts writing review articles and textbook chapters. DATA SOURCES: (1) MEDLINE search from 1966 to present; search terms used were myocardial infarction, clinical trials, multicenter studies, double-blind method, meta-analysis, and the text word "random:"; (2) references from pertinent articles and books; and (3) all editions of English-language general medical texts and manuals and review articles on treatment of myocardial infarction. STUDY SELECTION: Randomized control trials of therapies for reducing the risk of total mortality in myocardial infarction (acute and secondary prevention). Review articles and textbook chapters dealing with the general clinical management of patients with myocardial infarction. DATA EXTRACTION: Two authors read the material and recorded the results; disagreements were resolved by conference. DATA SYNTHESIS: We used the technique of cumulative meta-analysis (performing a new meta-analysis when the results of a new clinical trial are published) and compared the results with the recommendations of the experts for various treatments for myocardial infarction. Discrepancies were detected between the meta-analytic patterns of effectiveness in the randomized trials and the recommendations of reviewers. Review articles often failed to mention important advances or exhibited delays in recommending effective preventive measures. In some cases, treatments that have no effect on mortality or are potentially harmful continued to be recommended by several clinical experts. CONCLUSIONS: Finding and analyzing all therapeutic trials in a given field has become such a difficult and specialized task that the clinical experts called on to summarize the evidence in a timely fashion need access to better databases and new statistical techniques to assist them in this important task.

Humans↗
PubMed1992

Assessment of the efficacy and safety of antiarrhythmic therapy for chronic atrial fibrillation: observations on the role of trial design and implications of drug-related mortality.

The findings in clinical trials of antiarrhythmic drug efficacy and safety are frequently difficult to compare, since study design often has an important effect on trial outcome. To explore this problem further, we compared three designs--randomized control, nonrandomized control, and uncontrolled--collectively enrolling 2415 patients in 21 trials reporting on the role of quinidine in the prevention of chronic atrial fibrillation. The proportion of patients remaining in sinus rhythm at 3, 6, and 12 months after cardioversion was calculated by means of Kaplan-Meier techniques, and the data were pooled for each trial design. For the randomized control trials the difference in the absolute percentage of patients remaining in sinus rhythm in the quinidine and control groups was 24% at each of the three follow-up intervals. Contrary to findings in the randomized control trials, the magnitude of the treatment benefit in nonrandomized trials was smaller and declined markedly over time. The percentage of patients remaining in sinus rhythm in the uncontrolled trials was intermediate to the percentages in the other two trial designs. When the data from all three trial designs were pooled, the crude mortality rate was 2.0% in quinidine-treated patients and 0.6% in control patients. Sudden cardiac death or ventricular fibrillation was the cause of death in 13 of 19 patients for whom the cause of death was known, highlighting the potential risk of quinidine-induced proarrhythmia. Although quinidine is effective in maintaining sinus rhythm, estimates of the treatment effect vary among trial types.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Arrhythmia Agents↗
PubMed1992

Economic analysis in randomized control trials.

In medical technology assessment, randomized control trials (RCTs) play an important role in determining the relative efficacy of compared treatments. As scarce resources necessitate choosing among options for care, comparing costs of alternative tests, treatments, or programs also becomes important. This study assessed the prevalence and completeness of economic analyses in RCTs published from January 1966 through June 1988. It was found that only 121 of over 50,000 published randomized trials (0.2%) included economic analyses. For a random sample of 51 of these 121 studies, results revealed a mean quality of research score of 0.32 (SD of measurement = 0.14) and a mean economic analysis completeness score of 0.52 (SD = 0.13) on scales of 0 to 1. It was also found that higher economic completeness scores were positively correlated with later dates of publication (r = 0.28, P = 0.046) and with the presence of a statement of study perspective (r = 0.38, P = 0.006). A near-zero correlation between the economic completeness and the quality of research scores was revealed. Also noted were several deficiencies among the economic analyses, including improper allocation of overhead costs, absence of sensitivity analyses, and the fact that only 28% of the 51 studies included some form of aggregation of treatment costs and consequences. Progress in health care depends on accurate assessments of both relative efficacy and costs. The quality of both needs improvement.

Cost-Benefit Analysis↗
PubMed1992

Chlorination, chlorination by-products, and cancer: a meta-analysis.

OBJECTIVES: Individual epidemiological investigations into the association between chlorination by-products in drinking water and cancer have been suggestive but inconclusive. Enough studies exist to provide the basis for a meaningful meta-analysis. METHODS: An extensive literature search was performed to identify pertinent case-control studies and cohort studies. Consumption of chlorinated water, surface water, or water with high levels of chloroform was used as a surrogate for exposure to chlorination by-products. Relative risk estimates were abstracted from the individual studies and pooled. RESULTS: A simple meta-analysis of all cancer sites yielded a relative risk estimate for exposure to chlorination by-products of 1.15 (95% CI: 1.09, 1.20). Pooled relative risk estimates for organ-specific neoplasms were 1.21 (95% CI: 1.09, 1.34) for bladder cancer and 1.38 (95% CI: 1.01, 1.87) for rectal cancer. When studies that adjusted for potential confounders were pooled separately, estimates of relative risks did not change substantially. CONCLUSIONS: The results of this meta-analysis suggest a positive association between consumption of chlorination by-products in drinking water and bladder and rectal cancer in humans.

Case-Control Studies↗
PubMed1992

Oral hypoglycemic agents? Negative.

I am convinced that oral hypoglycemic therapy is associated with increased cardiovascular mortality. But the more important issue is whether the benefits of these agents are worth the risk.

Attitude of Health Personnel↗
PubMed1978

The importance of beta, the type II error and sample size in the design and interpretation of the randomized control trial. Survey of 71 "negative" trials.

Seventy-one "negative" randomized control trials were re-examined to determine if the investigators had studied large enough samples to give a high probability (greater than 0.90) of detecting a 25 per cent and 50 per cent therapeutic improvement in the response. Sixty-seven of the trials had a greater than 10 per cent risk of missing a true 25 per cent therapeutic improvement, and with the same risk, 50 of the trials could have missed a 50 per cent improvement. Estimates of 90 per cent confidence intervals for the true improvement in each trial showed that in 57 of these "negative" trials, a potential 25 per cent improvement was possible, and 34 of the trials showed a potential 50 per cent improvement. Many of the therapies labeled as "no different from control" in trials using inadequate samples have not received a fair test. Concern for the probability of missing an important therapeutic improvement because of small sample sizes deserves more attention in the planning of clinical trials.

Clinical Trials as Topic↗
PubMed1977

Evidence favoring the use of anticoagulants in the hospital phase of acute myocardial infarction.

Since the last comprehensive review of anticoagulation in acute myocardial infarction four additional randomized control trials have been reported. The overwhelming majority of all trials favored anticoagulation. Rates of thromboembolism were higher in the control, and hemorrhagic complications in the anticoagulated group. Pooling of all randomized control trials gives mean case fatality rates of 19.6% for the control and 15.4% for the anticoagulated group, a relative reduction of 21% (P less than 0.05 or less than 0.001, depending on the analytic method). Five of six randomized control trials reported "no effect" because the difference favoring anticoagulation was not statistically significant. However, sample sizes in these "negative" papers were too small to protect against missing a 21% reduction in true case fatality rate due to anticoagulation (beta greater than 0.10). All patients who present no specific contraindication should receive anticoagulants during hospitalization for infarction.

Acute Disease↗