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.
EERis the experimental (new treatment) event rate.CERis the control (old treatment or non-treatment) 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.
is the experimental (new treatment) event rate.
is the control (old treatment or non-treatment) event rate.
(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 |EER
— CER|/CER and accompanied by a 95% CI.
(absolute risk reduction) is the absolute arithmetic difference in bad
event rates between the experimental and control groups, calculated as
|EER — CER|.
(relative risk reduction) is the proportional reduction in bad event
rates between the experimental and control groups, calculated as |EER
— 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.
(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.
(absolute benefit increase) is the absolute arithmetic difference in
good event rates between the experimental and control groups, calculated as
|EER —CER|.
(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.
(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 that, if they
received the experimental treatment, would lead to 1 additional person being
harmed compared with the number of patients who received the control
treatment, calculated as 1/ARI, rounded up to the nearest whole number, and
accompanied by a 95% CI.
(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|.
(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.
(number needed to harm) is the number of patients that, if they
received the experimental treatment, would lead to 1 additional person being
harmed compared with the number of patients who received the control
treatment, calculated as 1/ARI, rounded up to the nearest whole number, and
accompanied by a 95% CI.