Risk reduction.

Risk reduction.

Risk

Risk terms:
Absolute risk = risk = incidence rate =
# of events in treated or control groups, divided by the number of people in the group
ARC = absolute risk of events in the control group
ART = the AR of events in the treatment group
ARR = Absolute risk reduction = absolute risk difference = risk difference = ARC – ART
RR = risk ratio = ART/ ARC
RRR = relative risk reduction = 1 – RR
NNT = number needed to treat = 1/ARR

Example chart.

Example chart.

What does this mean?

·         RR > 1 = events are more likely in the treatment group than the control group

·         RR < 1  = events are less likely in the treatment group than the control group

·         The closer the RR is to 1 the less significant of effect there is

·         Can interpret as % effect à RR of 0.67 = 1 – 0.67 = 33% less likely to die than those who did not receive steroids

·         When verbalizing risk ratios: try to say “RR times the risk of x in the treatment vs the control group” Eg: patients with CAP who received corticosteroids have 0.67 times the risk of death

NNT = 37 patients with CAP would have to be treated for 1 patient death to be prevented