53 - Clinical Trials in CVD Flashcards

1
Q

Why are clinical trials considered best to study causation?

A

Active change of exposure status.

Tightly-controlled study environment

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2
Q

Relative measures of intervention effect
1)
2)

A

1) Relative risks

2) Hazard ratios

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3
Q

Absolute measures of intervention effect
1)
2)

A

1) Absolute risk/rate reduction

2) Number needed to treat

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4
Q

Way to deal with confounders in a clinical trial

A

Randomisation

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5
Q

Way to deal with information bias

A

Blinding (single- or double-blind).

Reduces overseer bias.

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6
Q

Source of significant selection bias in clinical trials

A

Cross-over.
EG: sick patients drop out because they aren’t getting batter. Healthy patients stay in, so data appear to suggest greater effect of intervention.

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7
Q

Intention-to-treat analysis

A

A method of analysis for randomised trials in which all patients randomly assigned to one of the treatments are analysed together, regardless of whether or not they completed or received that treatment.

A way to minimise impact of cross-over

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8
Q

Difference between hazard ratio and relative risk

A

Hazard ratio applies to entire period of follow-up, is a weighted average of all measurements.
Relative risk is a risk at one point in time.

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9
Q

Survival analysis
1)
2)
3)

A

1) During follow up, note when occurrence of interest happens. Measure of interest is ‘time to event.’
2) Construct a Kaplan-Meier curve, which plots hazard or survival (1-hazard) vs time.
3) ‘Survival’ is avoidance of event of interest, not death.

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10
Q

Hazard

A

Continuously-updated ratio of event/no event

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11
Q

Hazard ratio

A

Hazard intervention:hazard control ratio.
EG: HR=0.5 means that at any point in time in follow up probability of outcome in intervention group is half that of in the control group

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12
Q

Risk/rate reduction

A

Change of outcome with exposure expressed in relative and absolute terms.

EG: Rate of outcome in control = 10/100
Rate of outcome in intervention = 7/100
Rate ratio = (7/100)/(10/100)=0.7
Absolute reduction = 10/100 - 7/100 = 3/100

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13
Q

Number needed to treat

A

Number of people that need to undergo treatment to prevent outcome in one.

Calculated by 1/(absolute risk or rate reduction)
EG: if absolute risk reduction is 3/100 per year, then 1/(3/100)=33.3. So 33.3 need to be treater/year to avert one case of outcome.

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14
Q

Big determinant of number needed to treat

A

How common condition is. If condition is rare, then a lot of people will need to be treated.

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15
Q

Name for NNT when intervention increases risk of developing outcome

A

Number needed to harm

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