# Clinical Trials in CVD Flashcards

1
Q

What is a clinical trial?

A

A longitudinal study that looks at an intervention and its effect on incidence - involves an intervention group and a control group

2
Q

What are the key outcomes of a clinical trial?

A

relative measures of intervention effect, absolute measures of intervention effect and survival analysis

3
Q

What are the three key features of clinical trials?

A

randomisation, blinding, intention to treat analysis

4
Q

What is randomisation?

A

A tool used to deal with confounding - random allocation of subjects into each arm of the clinical trial

5
Q

What is blinding?

A

A tool used to deal with information bias - means that the subject or the subject and the investigator are unaware of which arm of the clinical trial they are allocated to

6
Q

What is intention to treat analysis?

A

A tool used to deal with selection bias - means that you assume that participants remain in the group which they were assigned regardless of whether they did or not - introduces an overlap- will lead to an underestimate of the the true effect of the intervention

7
Q

What is a hazard?

A

A continually updated instantaneous rate to look at incidence in longitudinal studies e.g. week 1 10/1000 die, week 2 15/990 die etc.

8
Q

What is a survival analysis?

A

Looks at outcomes and their specific time of occurrence - typically done by plotting hazard against time on a kaplan-meier curve

9
Q

What is a hazard ratio?

A

Similar to relative risk but derived from statistical analysis and looks at whole period of follow up

10
Q

What does a hazard ratio of 0.5 mean?

A

That at any given point in time, the probability of the outcome for the intervention group was half that of the control group

11
Q

What is a risk/rate reduction?

A

The reduction of the outcome in either relative or absolute terms

12
Q

How is risk/rate reduction in relative terms calculated?

A

rate of outcome in intervention arm divided by rate of outcome in control arm e.g. 7/100py divided by 10/100py = 0.7

13
Q

How is risk/rate reduction in absolute terms calculated?

A

rate of outcome in control arm minus rate of outcome in intervention arm e.g. 10/100py - 7/100py = 3/100py

14
Q

What is the number needed to treat?

A

The number of people who are needed to undergo the intervention in order to prevent the outcome in one person

15
Q

How is the number needed to treat calculated?

A

1 divided by absolute risk/rate reduction e.g. 1 divided by 3/100py = 33.3

16
Q

What is number needed to harm?

A

The number of people who are treated to get one person who will get an unwanted outcome

17
Q

How is the number needed to harm calculated?

A

The same was as NNT, but when there is a negative absolute risk/rate reduction