The Science of Evidence Based Medicine

Question 1

What are the different types of studies?

Answer 1

Observation - Case control, cross sectional studies.

Experimental Studies - Randomised and non-randomised trials

Question 2

What are the different types of reviews?

Answer 2

Expert opinion, systematic review, meta-analysis

Question 3

What are case studies, series or case reports advantages and disadvantages?

Answer 3

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

Question 4

Describe cross sectional survey?

Answer 4

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

Question 5

Describe the advantages of cross sectional studies?

Answer 5

• Cheap and simple,
• Ethically safe,
• Useful in planning

Question 6

What are the disadvantages of a cross sectional study?

Answer 6

• Cause and effect?
• Volunteer bias,
• Unequal distribution of confounders

Question 7

What are some of the complications of studies?

Answer 7

Confounders - Uncontrolled extraneous variables.

Spurious association

Question 8

Descibe what a case control study is?

Answer 8

Where you compare histories from a patient and non patient group and draw conclusions

Question 9

What are the advantages of a case control study?

Answer 9

• 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.

Question 10

What are the disadvantages of case control studies?

Answer 10

• Retrospective study which relies on patient recall,
• Confounders,
• Selection of control group is difficult,
• Unlikely to detect rare causes of disease

Question 11

What is a cohort study?

Answer 11

It is where you follow a group of interest and a comparison group over a period of time and then compare outcomes.

Question 12

What are some advantages of a cohort study?

Answer 12

• Ethically safe,
• Subjects can be matched,
• Can show cause precedes the effect,
• Easier and cheaper than a randomised controlled trial.

Question 13

What are some of the disadvantages of cohort studies?

Answer 13

• 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

Question 14

What are randomised controlled trials?

Answer 14

Where patients are randomly allocated into a treatment and control croup.

Question 15

What is the difference between single and double blind studies?

Answer 15

Single - only the subjects don’t know what treatment they were receiving.

Double - Both subjects and investigators don’t know who is receiving treatment

Question 16

What are the advantages of a RCT

Answer 16

• Unbiased distribution of confounders,
• Clearly identified populations,
• Randomisation helps statistical analysis,
• More likely to be blinded

Question 17

What are the disadvantages of RCT?

Answer 17

• Expensive,
• Volunteer bias,
• Ethical issues if treatment group seen to respond better or badly

Question 18

How can can you establish a cause and effect?

Answer 18

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

Question 19

What are the advantages and disadvantages of expert review?

Answer 19

Advantages - Comprehensive survey and answer a specific question.

Disadvantages - Expert bias

Question 20

What is a systematic review?

Answer 20

It attempts to identify, appraise and synthesize all the empirical evidence that meets criteria to answer a questions

Question 21

Why are systematic reviews seen as the gold standard?

Answer 21

Avoidance and/or the minimisation of bias

Question 22

What are the advantages of a systematic review?

Answer 22

• 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.

Question 23

What are the disadvantages of systematic review?

Answer 23

• Dependent on screening strategy,
• Can be hard to compare results,
• Publication bias,
• Very time consuming

Question 24

What are the advantages of meta-analysis?

Answer 24

• Greater statistical power,
• Greater ability to extrapolate to the general population,
• Statistical analysis is more objective,
• More efficient to present a combined result

Question 25

What are the disadvantages of meta-analysis?

Answer 25

Individual studies don’t necessarily use the same methodology.

• Heterogeneity of study pop.
• Requires advanced statistical techniques,
• Time consuming