The Science of EBM

Question 1

• Observational studies

Answer 1

– Case control
– Cohort
– Cross sectional studies

Question 2

• Experimental studies

Answer 2

– Randomised and non-randomised trials

Question 3

Reviews

Answer 3

– Expert opinion
– Systematic Review
– Meta-analysis

Question 4

RTCs impossible

Answer 4

with treatments for very rare diseases where the number of patients is too limited

Question 5

RTCs unnecessary

Answer 5

when a treatment produces a ‘dramatic’ benefit - imatinib (Glivec) for chronic myeloid leukaemia

Question 6

RTCs stopping trials early

Answer 6

interim analyses of trials are now commonly undertaken to assess whether the treatment is showing benefit and if the trial can be stopped early

Question 7

RTCS resources

Answer 7

the costs of RCTs are substantial in money, time and energy

Question 8

confounders

Answer 8

• Uncontrolled extraneous variables
– Observation
Smokers tend to have smaller babies than non-
smokers

Question 9

Spurious association

Answer 9

• 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

Question 10

RTCs Generalisability

Answer 10

RCTs are often carried out on specific types of patients for a relatively short period of time

Question 11

Establishing cause and effect

Answer 11

1. Is the association due to a chance occurrence
2. Is it due to a flaw in the methodology (bias)
3. Is it to another factor which is linked to both
   the exposure and the outcome (confounder)

Question 12

What is a systematic review?

Answer 12

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.

Question 13

• Comprehensive literature search that identifies

Answer 13

all similar and relevant studies that satisfy pre-defined
– Inclusion criteria
– Exclusion criteria

Question 14

• Electronic databases

Answer 14

– Medline
– EMBASE
– Web of Science
– Cochrane register of controlled trials (CENTRAL) – US National Institutes of Health trails register

Question 15

Why are systematic reviews viewed as

the ’gold standard’?

Answer 15

Avoidance and/or the minimisation of bias

Question 16

what are the types of bias

Answer 16

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

Question 17

Meta analysis

Answer 17

Combine qualitative and quantitative study data from several selected studies to develop a single conclusion that has greater statistical power.

1. Establish statistical significance with studies that have conflicting results
2. Develop a more accurate estimate of effect magnitude
3. Provide a more complex analysis of harms, safety data, and benefits
4. Examine subgroups with individual numbers that are not statistically significant