week eight

Question 1

how can we express the results of binary studies

Answer 1

• Absolute risk reduction / increase (ARR/I)
  • Also called risk difference

– Relative risk (risk ratio)
– Relative risk reduction / increase (RRR/I)
– Number needed to treat/harm (NNT/H)

Question 2

Risk difference (RD) or Absolute risk reduction (ARR)

Answer 2

Is simply the difference in the proportion of subjects with the outcome of interest in each group.
– RD = X (control) – Y (intervention)

Question 3

risk ratio or relative risk

Answer 3

Is defined as the probability of an event in the active treatment group divided by the probability of an event in the control group.
– RR = Y/X or (intervention/control)

Question 4

relative risk reduction

Answer 4

RRR= 1-RR

Question 5

How to interpret risk ratios

Answer 5

A RR of 1 = no association between intervention/exposure and comparison
A RR < 1 = decreased risk of outcome among those receiving the intervention/exposure
A RR >1 = increased risk of outcome among those receiving the intervention/exposure

Question 6

number needed to treat

Answer 6

Is the number of patients you need to treat to prevent one additional bad outcome
NNT = 1/RD

Question 7

p Values

Answer 7

Traditionally p < 0.05 is used as a cut off for determining ‘statistical significance’

The p value quantifies the probability that an observed difference between two study groups might have arisen due to chance alone, assuming that there is in fact no difference between the groups

Question 8

confidence intervals

Answer 8

precision, they illustrate, allowing for the role of chance, how small or how large the true effect size might be

The narrower the confidence interval the more certain one can be about the size of the true effect