The Science of Evidence Based Medicine Flashcards
What are the different types of studies?
Observation - Case control, cross sectional studies.
Experimental Studies - Randomised and non-randomised trials
What are the different types of reviews?
Expert opinion, systematic review, meta-analysis
What are case studies, series or case reports advantages and disadvantages?
Advantages - Quick and cheap to conduct, rapid publication, early indicators of problems and can help detect new drug side effects.
Disadvantages - Statistically weak, no control group, very small numbers and cases may not be generalised to the wider population
Describe cross sectional survey?
Looking at a target population who do and no not have the outcome. It is usually a descriptive studies which may show an association between exposure and outcome
Describe the advantages of cross sectional studies?
- Cheap and simple,
- Ethically safe,
- Useful in planning
What are the disadvantages of a cross sectional study?
- Cause and effect?
- Volunteer bias,
- Unequal distribution of confounders
What are some of the complications of studies?
Confounders - Uncontrolled extraneous variables.
Spurious association
Descibe what a case control study is?
Where you compare histories from a patient and non patient group and draw conclusions
What are the advantages of a case control study?
- Simultaneously look at multiple risk factors,
- Good for studying rare conditions,
- Useful as initial studies to establish an association,
- Do not require a long follow up period.
What are the disadvantages of case control studies?
- Retrospective study which relies on patient recall,
- Confounders,
- Selection of control group is difficult,
- Unlikely to detect rare causes of disease
What is a cohort study?
It is where you follow a group of interest and a comparison group over a period of time and then compare outcomes.
What are some advantages of a cohort study?
- Ethically safe,
- Subjects can be matched,
- Can show cause precedes the effect,
- Easier and cheaper than a randomised controlled trial.
What are some of the disadvantages of cohort studies?
- High drop out rate,
- Exposure may be linked to a hidden confounder,
- blinding is difficult,
- Outcome of interest may take a long time to occur
What are randomised controlled trials?
Where patients are randomly allocated into a treatment and control croup.
What is the difference between single and double blind studies?
Single - only the subjects don’t know what treatment they were receiving.
Double - Both subjects and investigators don’t know who is receiving treatment
What are the advantages of a RCT
- Unbiased distribution of confounders,
- Clearly identified populations,
- Randomisation helps statistical analysis,
- More likely to be blinded
What are the disadvantages of RCT?
- Expensive,
- Volunteer bias,
- Ethical issues if treatment group seen to respond better or badly
How can can you establish a cause and effect?
- Association due to chance occurrence,
- Is it due to a flaw in methodology (bias),
- It is to another factor which is linked to both the exposure and the outcome
What are the advantages and disadvantages of expert review?
Advantages - Comprehensive survey and answer a specific question.
Disadvantages - Expert bias
What is a systematic review?
It attempts to identify, appraise and synthesize all the empirical evidence that meets criteria to answer a questions
Why are systematic reviews seen as the gold standard?
Avoidance and/or the minimisation of bias
What are the advantages of a systematic review?
- Uses explicit and reproducible methodology,
- Many different studies can be compared and contracted,
- Reduces bias as it takes into account range of views and findings,
- Less costly to review studies then start one.
What are the disadvantages of systematic review?
- Dependent on screening strategy,
- Can be hard to compare results,
- Publication bias,
- Very time consuming
What are the advantages of meta-analysis?
- Greater statistical power,
- Greater ability to extrapolate to the general population,
- Statistical analysis is more objective,
- More efficient to present a combined result
