The Science of EBM Flashcards
• Observational studies
– Case control
– Cohort
– Cross sectional studies
• Experimental studies
– Randomised and non-randomised trials
Reviews
– Expert opinion
– Systematic Review
– Meta-analysis
RTCs impossible
with treatments for very rare diseases where the number of patients is too limited
RTCs unnecessary
when a treatment produces a ‘dramatic’ benefit - imatinib (Glivec) for chronic myeloid leukaemia
RTCs stopping trials early
interim analyses of trials are now commonly undertaken to assess whether the treatment is showing benefit and if the trial can be stopped early
RTCS resources
the costs of RCTs are substantial in money, time and energy
confounders
• Uncontrolled extraneous variables
– Observation
Smokers tend to have smaller babies than non-
smokers
Spurious association
• Is ultrasound harmful to the fetus?
– Initial studies showed that babies exposed to
ultrasound had lower birth weights
– Later studies failed to confirm this observation
RTCs Generalisability
RCTs are often carried out on specific types of patients for a relatively short period of time
Establishing cause and effect
- Is the association due to a chance occurrence
- Is it due to a flaw in the methodology (bias)
- Is it to another factor which is linked to both
the exposure and the outcome (confounder)
What is a systematic review?
A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre- specified eligibility criteria to answer a given research question.
Researchers conducting systematic reviews use explicit methods aimed at minimizing bias, in order to produce more reliable findings that can be used to inform
decision making.
• Comprehensive literature search that identifies
all similar and relevant studies that satisfy pre-defined
– Inclusion criteria
– Exclusion criteria
• Electronic databases
– Medline
– EMBASE
– Web of Science
– Cochrane register of controlled trials (CENTRAL) – US National Institutes of Health trails register
Why are systematic reviews viewed as
the ’gold standard’?
Avoidance and/or the minimisation of bias
what are the types of bias
Selection bias Performance bias Attrition bias
Detection bias
Reporting bias Publication bias Time-lag bias
Language bias
Funding bias
Citation bias
Developed country bias Multiple publication bias
Meta analysis
Combine qualitative and quantitative study data from several selected studies to develop a single conclusion that has greater statistical power.
- Establish statistical significance with studies that have conflicting results
- Develop a more accurate estimate of effect magnitude
- Provide a more complex analysis of harms, safety data, and benefits
- Examine subgroups with individual numbers that are not statistically significant
