The glossary below provides definitions for several terms found
in the structured abstracts of the Evidence-Based Orthopaedics section,
many of which may not be familiar to orthopaedic surgeons.
The following terms are commonly used in abstracts describing
trials of therapeutic interventions.
EER is the experimental (new treatment) event rate.
CER is the control (old treatment or nontreatment)
event rate.
CI (confidence interval) quantifies the uncertainty
in measurement. CI is usually reported as a 95% CI, which is the
range of values within which we can be 95% sure that the true value
for the whole population lies.
When the experimental treatment reduces the risk for
a bad event:
ARR (absolute risk reduction) is the absolute arithmetic
difference in bad event rates between the experimental and control
groups, calculated as |EER - CER|.
RRR (relative risk reduction) is the proportional
reduction in bad event rates between the experimental and control
groups, calculated as |ERR - CER|/CER and accompanied by a 95% CI.
When trying to interpret the benefit of a new therapy,
the NNT can be helpful to clinicians.
NNT (number needed to treat) is the number of patients
who need to be treated to prevent 1 additional bad outcome, calculated
as 1/ARR, rounded up to the nearest whole number, and accompanied
by a 95% CI.
When the experimental treatment increases the probability
of a good event:
ABI (absolute benefit increase) is the absolute
arithmetic difference in good event rates between the experimental
and control groups, calculated as |EER -CER|.
RBI (relative benefit increase) is the proportional
increase in good event rates between the experimental and control
groups, calculated as |EER - CER|/CER and accompanied by a 95% CI.
NNT (number needed to treat) is the number of patients
who need to be treated to achieve 1 additional favorable outcome,
calculated as 1/ARR, rounded up to the nearest whole number, and
accompanied by a 95% CI.
When the experimental treatment increases the probability
of a bad event:
ARI (absolute risk increase) is the absolute arithmetic
difference in bad event rates between groups, when the experimental
treatment harms more patients than the control treatment, calculated
as |EER - CER|.
RRI (relative risk increase) is the proportional
increase in bad event rates between the experimental and control
groups, calculated as |EER - CER|/CER and accompanied by a 95% CI.
NNH (number needed to harm) is the number of patients
who, if they received the experimental treatment, would lead to
1 additional person being harmed compared with patients who received
the control treatment, calculated as 1/ARI, rounded up to the nearest whole
number, and accompanied by a 95% CI.