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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↗
PubMed1991

Problems induced by meta-analyses.

Over 150 meta-analyses of randomized control trials have so far been published in the English language, and new ones are appearing at a rate of over fifteen per year. This explosion of a relatively new method of evaluating clinical medicine presents a number of challenges to statisticians and those responsible for health care policy. The pitfalls of retrospective research must be avoided, and the quality of the original trials should be evaluated. Heterogeneity of the control event rates and the treatment differences need to be dealt with statistically. Most important are the problems raised by the need to update meta-analyses as new trials are published.

Clinical Trials as Topic↗
PubMed1991

Can meta-analysis help uncertainty in surgery for otitis media in children.

While otitis media is perhaps the most common disease of childhood that receives medical attention, there is little agreement concerning the efficacy of the medical and surgical therapies employed to try to alleviate its symptoms or hasten its natural resolution. Because various surgeries including adenoidectomy, myringotomy, and insertion of tympanostomy tubes are frequently involved in the treatment of otitis media with effusion (OME), it is likely the most expensive condition being managed in national terms. In an attempt to elucidate the most appropriate management of this condition, a meta-analysis was attempted to the 12 randomized control trials of surgical treatments for OME in children, published between 1966 and 1990. Heterogeneity both in the populations and comparisons studied and in the outcomes presented made meta-analysis an inappropriate method for clarifying this area of clinical uncertainty. Important elements in the design of randomized control trials that should be included in future studies of treatment for OME are therefore discussed.

Adenoidectomy↗
PubMed1990

Endoscopic hemostasis. An effective therapy for bleeding peptic ulcers.

We performed a meta-analysis of 25 randomized control trials that compared endoscopic hemostasis with standard therapy for bleeding peptic ulcer. For recurrent or continued bleeding, the mean rate in control patients was 0.39, and the pooled rate difference, or reduction due to therapy, was 0.27 +/- 0.15 (95% confidence interval) (69% relative reduction). For emergency surgery, the mean rate in control patients was 0.26, and the pooled rate difference was 0.16 +/- 0.05 (62% relative reduction). Most important, for overall mortality, the mean rate in control patients was 0.10, and the pooled rate difference was 0.03 +/- 0.02 (30% relative reduction). The effects were greatest in patients with spurting or visible blood vessels and equivocal when the ulcer showed only signs of recent bleeding. We conclude that endoscopic hemostasis is clearly effective but that data were insufficient for direct comparisons between modalities. Randomized control trials to compare the different modes of endoscopic therapy should continue.

Adult↗
PubMed1990

A cohort study of summary reports of controlled trials.

Substantial numbers of clinical trials continue to be reported only in summary reports that present insufficient methodological details to permit informed judgments about the likely validity of the conclusions. Using a cohort of 176 controlled trials reported in summary form, we tested the hypotheses that they would be more likely to be followed by full reports if, on the basis of the information provided in the summary report, (1) the trial was judged to be methodologically sound, (2) the results favored the test treatment, and (3) the sample size was relatively large. The results of univariate and multivariate analyses provided support for only the third of these hypotheses. Investigators, as well as those who fund and sanction the conduct of clinical research, should make greater efforts to ensure that clinical trials are reported properly.

Clinical Trials as Topic↗
PubMed1990

A meta-analysis of alcoholic beverage consumption in relation to risk of colorectal cancer.

Quantitative methods were used to review epidemiologic data relating consumption of alcoholic beverages to risk of colorectal cancer. The data (27 studies) supported the presence of a weak association. For consumption of two alcoholic beverages daily, on average the relative risk of colorectal cancer was 1.10 (95% confidence interval 1.05-1.14). Other findings were: (1) the association did not vary according to gender or site within the large bowel; (2) results from follow-up studies (relative risk 1.32, 95% confidence interval 1.16-1.51) suggested a stronger relationship than those from case-control studies (relative risk 1.07, 95% confidence interval 1.02-1.12); and (3) the evidence supporting beverage specificity was not conclusive, although the results were consistent with a stronger association with consumption of beer (relative risk 1.26, 95% confidence interval 1.13-1.41) than with consumption of wine (relative risk 1.11, 95% confidence interval 0.91-1.36) or liquor (relative risk 1.13, 95% confidence interval 0.99-1.29). Because the magnitude of the association between alcohol consumption and risk of colorectal cancer was small, the findings regarding a causal role of alcohol were inconclusive.

Alcohol Drinking↗
PubMed1990

Dipyridamole in the treatment of angina pectoris: a meta-analysis.

A meta-analysis of 11 randomized trials published between 1960 and 1970 was performed to re-evaluate data on the efficacy of dipyridamole in the prevention and treatment of chronic angina pectoris. Three trials significantly favored drug vs placebo, four showed a trend towards drug vs placebo, two showed no difference and two showed a trend towards placebo vs drug. The combined results of these 11 trials showed a statistically significant improvement with dipyridamole. Although this result should be viewed with caution because of methodologic variations in the studies, the available evidence appears to suggest that dipyridamole may have a beneficial effect, and that it may have been prematurely discarded in the treatment of angina pectoris.

Angina Pectoris↗