Understanding Evidence

doi:10.1017/9781316286234.003

Chapter 2 - Understanding Evidence

from Part I - Foundations

Published online by Cambridge University Press: 15 December 2020

Jeffrey L. Saver and

Graeme J. Hankey

Edited by

Jeffrey L. Saver and

Graeme J. Hankey

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Jeffrey L. Saver: Affiliation:
David Geffen School of Medicine, University of Ca
Graeme J. Hankey: Affiliation:
University of Western Australia, Perth

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Summary

Almost all efficacious stroke treatments confer moderate-to-large benefits, but not staggeringly huge benefits. However, moderate treatment effects can be clinically very worthwhile for the patient. To detect moderate-large treatment benefits, trials must avoid bias and random error. Studies with weak designs (personal experience, observational studies with historical controls, and observational studies with concurrent, non-randomized controls) will not sufficiently control bias and random error to enable reliable discrimination of a true moderate-to-large benefit from false positives and false negatives. Randomized clinical trials are required. 'Ingredients' for a good trial – Proper randomization and concealment of allocation (i.e. clinician cannot have foreknowledge of next treatment allocation)/Outcome evaluation blind to the allocated treatment/Analysis by allocated treatment (including all randomized patients: intention-to-treat)/Large numbers of major outcomes and correspondingly narrow CIs/Conclusion based on pre-specified primary hypothesis and outcome/Chief emphasis on findings in overall study population. Advantages of systematic reviews (over traditional unsystematic, narrative reviews) – Use explicit, well-developed methods to reduce bias/Summarize large amounts of data explicitly/Provide all available data/Increase statistical power and precision/Look for consistencies/inconsistencies/Improve generalizability. Cochrane Reviews – Generally higher quality than other systematic reviews/Periodically updated/Available over internet/Abstracts available free of charge/Full reviews available free of charge in over 100 low- and middle-income countries

Keywords

Evidence-based medicine bias randomized trials systematic reviews meta-analysis subgroups forest plots outcome measures number needed to treat odds ratio

Information

Type: Chapter
Information: Stroke Prevention and Treatment
An Evidence-based Approach
, pp. 10 - 34

DOI: https://doi.org/10.1017/9781316286234.003 [Opens in a new window]

Publisher: Cambridge University Press

Print publication year: 2020

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