Updated on 30.10.2016.
Evidence Based unbiased information
Evidence Based Medicine (EBM) has become a popular phrase over the last couple of decades. A “Good Doctor” must practice Evidence Based Medicine. To do that effectively every Doctor must have a clear understanding of what is EBM, what is not EBM, the levels of evidence, Randomised Controlled Trial (RCT), how to eliminate bias during trials, Tests of significance etc. This article has included information in regard to those topics.
What you need to know about
“Evidence Based Medicine” – themedideas Facts & Figures
What is Evidence-Based Medicine?
It is the conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients by intregrating individual clinical expertise with the best available external clinical evidence from systematic research (Sackett et al, 1996).
What Evidence-Based Medicine is not?
It does not replace or detract from individual clinical expertise; the proficiency, judgement and surgical skills that we gain only through observation and supervised practice (Sackett et al, 1996).
What are the levels of evidence?
There are five levels of evidence:
Level I: Strong evidence from at least one systematic review of multiple, well-designed randomised controlled trials
Level II: Strong evidence from at least one properly designed randomised controlled trial of appropriate size
Level III: Evidence from well-designed trials without randomisation, single group pre-post, cohort, time series or matched case-controlled studies
Level IV: Evidence from well-designed non-experimental studies from more than one centre or research group
Level V: Opinions of respected authorities, based on clinical evidence, descriptive studies or reports of expert committees
The Royal College of Obstetricians and Gynaecologists, London uses three levels of evidence:
Grade A: Randomised controlled trials (Levels I & II)
Grade B: Other robust experimental or observational studies (Levels III & IV)
Grade C: More limited evidence but the advice relies on expert opinion and has the endorsement of respected authorities (Level V)
Why Randomised Controlled Trial
provides the best evidence?
1. Because this is the only way to avoid known and unknown selection biases (systematic errors) that weaken the observational studies.
2. It does not guarantee that the comparison groups will be exactly matched in respect of all characteristics of prognostic importance. But it does guarantee that the subjects of the comparison groups will be selected by chance rather than by any biased selection.
3. That is why it is considered to be the methodological ‘gold standard’ for comparing alternative forms of care.
4. A randomised controlled trial does not always guarantee the absence of selection bias unless selective recruitment into and withdrawal from the study are excluded with certainty.
What are other ways to minimise biases?
1. ‘Masking’ or ‘blinding’ can minimise the bias which results when those receiving, providing or evaluating care know which of the alternative forms of care has been received. When all of those receiving, providing or evaluating care are blinded it is called “Double Blind” Trial.
2. It is particularly useful when one or more of the forms of care is likely to have psychologically mediated (placebo) effects on the outcome of interest.
3. It also minimises the ability of the caregiver to adjust the remainder of their care in the light of their knowledge of the initial part of the study.
4. Bias may arise from the assessor’s knowledge of which form of care has been received. This may be eliminated by having the outcomes assessed by independent observers who are not aware of the forms of care allocation.
(NB – An example of double-blind randomised controlled trial was ORACLE Trial)
What other factor
can give misleading results?
1. Random errors (the play of chance) may give misleading results despite avoiding selection biases.
2. Random errors (the play of chance) are reduced by increasing the sample size.
3. Tests of significance (such as T-Test, Chi Square Test etc) are used to assess the likelihood of the observed differences between the alternative forms of care being a reflection of random errors.
4. The statistical significance is expressed by the p value or confidence interval.
1. Cooke IE. Finding the evidence. In: Cooke IE, Sackett DL, ed. Bailliere’s Clinical Obstetrics and Gynaecology International Practice and Research Vol 10, Evidence-based Obstetrics and Gynaecology. London: WB Saunders, 1996: 551-67.
2. Crowley P. Using an overview. In: Cooke IE, Sackett DL, ed. Bailliere’s Clinical Obstetrics and Gynaecology International Practice and Research Vol 10, Evidence-based Obstetrics and Gynaecology. London: WB Saunders, 1996: 585-97.
3. Sackett DL, Rosenberg WMC, Gray JAM et al. Evidence-based Medicine: what it is and what it isn’t. Br Med J, 1996; 312: 71-2.
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© Dr Sudipta Paul, themedideas.com, 2013