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absolute risk increase
(ARI) The increase in risk with a new therapy compared with
the risk without the new therapy.
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absolute risk reduction
(ARR) The reduction in risk with a new therapy compared with
the risk without the new therapy; it is the absolute value of the
difference between the experimental event rate and the control event
rate (EER – CER).
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absolute value The
positive value of a number, regardless of whether the number is
positive or negative. The absolute value of a is symbolized a.
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actuarial analysis See life table analysis.
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addition rule The
rule which states the probability that two or more mutually exclusive
events all occur is the sum of the probabilities of each individual
event.
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adjusted rate A
rate adjusted so that it is independent of the distribution of a
possible confounding variable. For example, ageadjusted rates are
independent of the age distribution in the population to which they
apply.
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agespecific mortality
rate The mortality rate in a specific age group.
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alpha (α) error See type I error.
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alpha (α) value The level
of alpha (α) selected in a hypothesis test.
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alternative hypothesis The
opposite of the null hypothesis. It is the conclusion when the null
hypothesis is rejected.
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analysis of covariance
(ANCOVA) A special type of analysis of variance or regression
used to control for the effect of a possible confounding factor.
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analysis of residuals In
regression, an analysis of the differences between Y and Y
′ to
evaluate assumptions and provide guidance on how well the equation
fits the data.
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analysis of variance
(ANOVA) A statistical procedure that determines whether any
differences exist among two or more groups of subjects on one or
more factors. The F test
is used in ANOVA.
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backward elimination A
method to select variables in multiple regression that enters all
variables into the regression equation and then eliminates the variable
that adds the least to the prediction, followed by the other variables
one at a time that decrease the multiple R by the least amount until all statistically
significant variables are removed from the equation.
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bar chart or bar
graph A chart or graph used with nominal characteristics to
display the numbers or percentages of observations with the characteristic
of interest.
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Bayes’ theorem A
formula for calculating the conditional probability of one event, P(A

B), from the conditional
probability of the other event,
P(B

A).
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bellshaped distribution A
term used to describe the shape of the normal (gaussian) distribution.
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beta (β) error See type II error.
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