Absolute Risk Difference is the arithmetic
difference between the rates of events in the intervention
and control group.
Absolute Risk Reduction refers to the decrease
of a bad event as a result of the intervention.
Absolute Benefit Increase refers to the increase
of a good event as the result of the intervention.
Confidence Intervals are calculated on the
results of the data to show the strength or weakness
of the evidence. A 95%CI[range] means that if you
were to repeat the same clinical trial a hundred
times you can be 95% sure that the data would fall
within the calculated range.
Intention to treat analysis of patients with
the treatment group to which they were originally
assigned, regardless of whether or not they actually
received the treatment or not.
Likelihood Ratio indicates the likelihood
that a given test result would be expected in a patient
with the target disorder compared to the likelihood
that the same result would be expected in a patient
without that disorder.
Numbers Needed to Treat (NNT) the number
of patients who need to be treated to prevent one
bad outcome. The NNT is a useful number when you
want to compare the costs and adverse effects of
a treatment with its benefits.
Odds Ratio describes the odds of an experimental
patient suffering an adverse event relative to a
P Value refers to the probability that any
particular outcome would have arisen by chance. (The
smaller the P value the less likely the data was
by chance.) Standard scientific practice, usually
deems a P value of less than 1 in 20 (expressed as
P=.05) as "statistically significant". The smaller
the P value the higher the significance. A P value
of P=.01 ( less than 1 in 100) is considered "statistically
Predictive Value of tests: In screening and
diagnostic tests, the probability that a person with
a positive test is a true positive (i.e., has the
disease), is referred to as the positive Predictive
Value; whereas, the Negative Predictive Value is
the probability that the person with a negative test
does not have the disease. Predictive value is related
to the sensitivity and specificity of the test.
Relative Risk is the risk of developing a
disease in the exposed group divided by the risk
of developing the disease in the unexposed group.
Relative Risk Reduction is the proportional
difference between the rates of events in the control
group and the intervention group. Relative Risk Reduction
is usually a larger number than the Absolute Risk
Difference and therefore tends to exaggerate the
Sensitivity measures the proportion of patients
with the disease who also test positive for the disease.
Specificity measures the proportion of patients
without the disease who also test negative for the
A good test is both highly sensitive and highly
See also the Glossary
of Terms from Evidence Based Emergency Medicine and the New
York Academy of Medicine
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