PubMed · 7442594
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H Begemann. 1980-11-07. [The placebo problem].. https://pubmed.ncbi.nlm.nih.gov/7442594/
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BACKGROUND: Endoscopic injection of normal saline solution is reportedly an effective treatment for bleeding ulcers. If it is as effective as standard therapy, low cost, wide availability, and lack of injury would make saline solution injection an attractive option. METHODS: Patients with clinical evidence of major bleeding from an ulcer with active bleeding or a nonbleeding visible vessel were randomly assigned to injection with normal saline solution (1-2 mL boluses; mean volume 30 mL) or bipolar electrocoagulation (20 W, 10-sec applications; mean time 100 sec). Patients, those caring for patients, and those collecting data were blinded to therapy. RESULTS: Further bleeding occurred in 14 (29%) of 48 patients in the saline solution group versus 6 (12%) of 52 patients in the bipolar group (95% CI [2%, 33%]; p = 0.04). Significantly more units of blood were transfused in the saline solution group (median 2 units vs. 0 units; p = 0.01). Hospital days (median 4 vs. 3) and mortality (6% vs. 2%) were not significantly different in the 2 groups. Independent risk factors for further bleeding were saline solution injection (p = 0.02), units transfused before therapy (p = 0.02), and ulcer size (p = 0.03). CONCLUSION: Local tamponade with saline solution injection is less effective than bipolar electrocoagulation for the treatment of bleeding ulcers.
PURPOSE: To explore whether reported methodologic quality affects estimated intervention effects in randomized trials and contributes to discrepancies between the results of large randomized trials and small randomized trials in meta-analyses. DATA SOURCES: Meta-analyses of randomized trials that included at least one large trial (>/=1000 participants) were included, regardless of the therapeutic area. Eligible meta-analyses were identified through electronic searches and bibliographies of relevant articles. STUDY SELECTION: Full-length randomized trials. DATA EXTRACTION: Methodologic quality was assessed according to reported randomization, double blinding, and follow-up as separate components and by using the Jadad composite scale. DATA SYNTHESIS: Fourteen meta-analyses involving 190 randomized trials from eight therapeutic areas were included. Compared with large trials, intervention effects were exaggerated in small trials with inadequate allocation sequence generation (ratio of odds ratios, 0.46 [95% CI, 0.25 to 0.83]; P = 0.011), inadequate allocation concealment (ratio of odds ratios, 0.49 [CI, 0.27 to 0.86]; P = 0.014), and no double blinding (ratio of odds ratios, 0.52 [CI, 0.28 to 0.96]; P = 0.01). Large trials did not differ significantly from small trials with adequate generation of the allocation sequence, adequate allocation concealment, or adequate double blinding. No association was seen between reported follow-up and intervention effects. The Jadad scale provided no additional information because the scale and the quality components overlapped substantially. CONCLUSIONS: Inadequate generation of the allocation sequence, allocation concealment, and double blinding lead to exaggerated estimates of intervention benefit and may contribute to discrepancies between the results of large randomized trials and small randomized trials in meta-analyses.
The information needed to determine the internal and external validity of an experimental study is discussed. Internal validity is the degree to which a study establishes the cause-and-effect relationship between the treatment and the observed outcome. Establishing the internal validity of a study is based on a logical process. For a research report, the logical framework is provided by the report's structure. The methods section describes what procedures were followed to minimize threats to internal validity, the results section reports the relevant data, and the discussion section assesses the influence of bias. Eight threats to internal validity have been defined: history, maturation, testing, instrumentation, regression, selection, experimental mortality, and an interaction of threats. A cognitive map may be used to guide investigators when addressing validity in a research report. The map is based on the premise that information in the report evolves from one section to the next to provide a complete logical description of each internal-validity problem. The map addresses experimental mortality, randomization, blinding, placebo effects, and adherence to the study protocol. Threats to internal validity may be a source of extraneous variance when the findings are not significant. External validity is addressed by delineating inclusion and exclusion criteria, describing subjects in terms of relevant variables, and assessing generalizability. By using a cognitive map, investigators reporting an experimental study can systematically address internal and external validity so that the effects of the treatment are accurately portrayed and generalization of the findings is appropriate.