Randomised Control Trials

Question 1

what are the advantages of randomised control trials?

Answer 1

• intervention and control groups will be similar in all respects (except the intervention), minimising selection bias and confounding.
• if the participants are blind to the treatment allocation, reporting bias can be minimised
• if the investigators are blind to the allocation, observer bias can be minimised
• multiple outcomes can be examined
• the incidence rates of the outcome can be measured

Question 2

disadvantages of randomised control trials?

Answer 2

• expensive to conduct
• intervention studies are impossible to conduct for ethical/logistical reasons in some situations
• time-consuming

Question 3

what are the main components of a randomised control trial?

Answer 3

population

intervention

comparator

outcome

Question 4

what is restricted randomisation?

Answer 4

refers to any procedure used with random assignment to achieve balance between study groups in size or baseline characteristics

Question 5

what is block randomisation?

Answer 5

computer generates complete blocks

ensures that the number of participants allocated to each group is equal after every block of x patients has entered the trial

Question 6

what is stratified randomisation?

Answer 6

useful if other risk factors have a strong influence on the outcome

Question 7

what is allocation concealment?

Answer 7

refers to making sure that the method of allocating a participant to a group can’t be revealed

(e.g. intervention, placebo, intervention, placebo…)

Question 8

what are the advantages of parallel group trials?

Answer 8

• easily applicable and understood
• multiple groups can be studied
• easier to multi-centre studies

Question 9

what are the disadvantages of parallel group trials?

Answer 9

• larger sample size
• more expensive
• with multiple groups may be difficult to analyse

Question 10

what are the advantages of crossover trials?

Answer 10

• fewer patients needed
• eliminates between patient variability
• test is within-patient, so balanced
• can reduce ethical issues with placebo

Question 11

what are the disadvantages of crossover trials?

Answer 11

• carry-over effects possible
• cant be used in curable treatments or for long-term treatment
• data wasted when patients drop out in first period
• duration of trial longer

Question 12

what are the advantages of factorial trials?

Answer 12

can assess combined effects in one trial

Question 13

what are the disadvantages of factorial trials?

Answer 13

• interaction effects
• more difficult to meet inclusion criteria
• complex

Question 14

what is cluster randomisation?

Answer 14

when people are organised in natural groups (i.e. clusters)

clusters are randomised, not individuals

Question 15

what are the disadvantages of cluster randomisation?

Answer 15

• need to randomise many clusters
• need increased sample size
• subjects within a cluster may be different to subjects in other clusters
• allocation concealment is more difficult
• analysis is more complicated

Question 16

what is performance bias?

Answer 16

systematic differences in the care provided to the participants in the comparison groups other than the intervention under investigation.

often intervention receive more attention that the controls, particularly if not blinded.