RCT

Question 1

What are RCT used to evaluate?

Answer 1

Treatment effectiveness

They inform guidelines

Question 2

Define the components of internal validity of a study

Answer 2

A causal relationship between the two variables must be properly demonstrated.

• Observation
• Explanation of the observation

Eliminate:

1) Bias - the way you assess the outcome could influence the outcome
2) Confounding - another factor in the trial affects it
3) Chance - could it happen by chance/fluke

If not: hypothesis is correct

Question 3

What is external validity?

Answer 3

Is it applicable to my patient population? Generalisability

Question 4

Should you treat? Four considerations

Answer 4

• Benefit worth harm?
• Resource costs - ?better use of resources
• Patient preferences
• Ethics

Question 5

Name three types of intervention studies

Answer 5

1) Before and after intervention - assess the group before treatment and after
2) Intervention groups compared to control - assess before and after but compare to non-intervention group
3) RCT - groups allocated at random and compare to control

Question 6

What is regression to the mean?

Answer 6

When you observe an extreme value this is partially due to chance. The next observation is likely to be closer to the mean -> can give the appearance of improvement.

Get a control group

Question 7

What issues do ‘before and after studies’ have?

Answer 7

Assess a group of pts before and after - bus
bias - expectations things would be better
confounding - disease may get better on its own anyway
chance

Question 8

What issues to intervention and control studies have?

Answer 8

They compare effectiveness with the control group which is good! but…
bias - pt or researcher beliefs can affect outcome measure
confounding - differences between the start groups?, were they treated differently?
chance

Question 9

Define double-blinded

Answer 9

Participants and assessors do not know what group they’re in

Question 10

What is randomisation?

Answer 10

Use chance allocation - any differences are allocated by chance.
Confounders are distributed by chance (both known and unknown)

Question 11

What outcome measures are used in RCTs?

Answer 11

Clinical effectiveness - cure/recovery

Patient experience - QoL, pain score

Question 12

What are the ethical considerations for RCTs?

Answer 12

Are pts being disadvantaged by being in the control or the intervention group?

Question 13

What is clinical equipoise?

Answer 13

If you think one treatment is better (placebo or intervention) you cannot ethically randomise.

Question 14

What are the choices for control?

Answer 14

Usual care
Placebo
Nothing

Question 15

What is contamination in an RCT (crossover)?

Answer 15

Pts randomised to the control may accidentally receive the intervention or visa versa

Question 16

How can contamination be managed in an RCT?

Answer 16

1) Analyse according to treatment received (but this causes allocation bias
2) Analyse according to intention to treat - preferred but may underestimate effect
Difficult in information studies
Can reduce by cluster randomisation

Question 17

What is relative risk, how do you calculate it?

Answer 17

probability of the event in the treatment arm/probability of event in the control arm

Question 18

What does a relative risk of 0.88 mean?

Answer 18

The risk is less in the treatment arm. The intervention reduces the risk of the measured outcome by 12%

Question 19

How do you calculate the probability of an event in the treatment arm?

Answer 19

events/total number of people in treatment arm

Question 20

How do you calculate absolute risk (risk difference)?

Answer 20

probability of an event in the treatment arm - probability of event in the control group

Question 21

What does an absolute risk (difference) of -0.017 mean?

Answer 21

You are 1.7% less likely to die (experience outcome) on the intervention

Question 22

What does a number needed to treat of 41 mean?

Answer 22

Treating 41 people would save 1 person from outcome

Question 23

How do you calculate NNT?

Answer 23

1/absolute risk (ignore the negative sign)

Question 24

What causes bias in assessing outcome?

Answer 24

pt, researcher and analysts expectations - ideally blind them
Can conceal allocation

Question 25

When are losses to follow up an issue?

Answer 25

If treatment allocation (to intervention) and outcomes cause drop out - everyone who gets treatment dies!

Question 26

When might you need a large sample size?

Answer 26

Measured effect is small - need a large sample size
Measured imprecisely
Consider the significance level