Randomised Trials and Other Evidence

Question 1

What are ‘parallel groups’ when used in randomised trials?

Answer 1

when the effect of a treatment is curative (non-reversible)

Question 2

What are ‘cross-over groups’ when used in randomised trials?

Answer 2

when the treatment effect is reversible

Question 3

What are the advantages of cross-over trials vs parallel groups trials?

Answer 3

• Fewer participants needed
• Allows qualitative data to be sued to avoid ‘scores’ or quantifying subjective symptoms
• Compares 2 drugs in the same individual rather than one drug in two different people
• Can omit non-compliers in the analysis as the participant is their own control

Question 4

What is an interventional study design?

Answer 4

parallel or cross-over randomised trial

Question 5

What is an observational study design?

Answer 5

cohort (prospective) or case control (retrospective study)

Question 6

What are the pros and cons of cohort studies?

Answer 6

• Rigorous
• Long duration
• Large size required
• Susceptible to confounders

Question 7

What are the pros and cons of case-control studies?

Answer 7

• Quick
• Small numbers needed
• Susceptible to bias – especially recall bias
• Susceptible to confounders

Question 8

What is an odds ratio?

Answer 8

The odds of an event to the odds of the non-event

Question 9

What is ‘relative risk’?

Answer 9

The risk of an event happening against the whole group

Question 10

What’s the difference between an odds ratio and a relative risk?

Answer 10

• Odds ratio – the odds of an event to the odds of the non-event
• Relative risk – the risk of an event happening against the whole group