prev {riskyr} | R Documentation |
The prevalence (baseline probability) of a condition.
Description
prev
defines a condition's prevalence value
(or baseline probability):
The probability of the condition being TRUE
.
Usage
prev
Format
An object of class numeric
of length 1.
Details
Understanding or obtaining the prevalence value prev
:
Definition:
prev
is the (non-conditional) probability:prev = p(condition = TRUE)
or the base rate (or baseline probability) of the condition's occurrence or truth.
In terms of frequencies,
prev
is the ratio ofcond_true
(i.e.,hi + mi
) divided byN
(i.e.,hi + mi
+fa + cr
):prev = cond_true/N = (hi + mi)/(hi + mi + fa + cr)
Perspective:
prev
classifies a population ofN
individuals by condition (prev = cond_true/N
).prev
is the "by condition" counterpart toppod
(when adopting a "by decision" perspective) and toacc
(when adopting a "by accuracy" perspective).Alternative names: base rate of condition, proportion affected, rate of condition
= TRUE
cases.prev
is often distinguished from the incidence rate (i.e., the rate of new cases within a certain time period).Dependencies:
prev
is a feature of the population and of the condition, but independent of the decision process or diagnostic procedure.While the value of
prev
does not depend on features of the decision process or diagnostic procedure,prev
must be taken into account when computing the conditional probabilitiessens
,mirt
,spec
,fart
,PPV
, andNPV
(as they depend onprev
).
References
Consult Wikipedia for additional information.
See Also
prob
contains current probability information;
num
contains basic numeric variables;
init_num
initializes basic numeric variables;
comp_prob
computes derived probabilities;
comp_freq
computes natural frequencies from probabilities;
is_prob
verifies probabilities.
Other probabilities:
FDR
,
FOR
,
NPV
,
PPV
,
acc
,
err
,
fart
,
mirt
,
ppod
,
sens
,
spec
Other essential parameters:
cr
,
fa
,
hi
,
mi
,
sens
,
spec
Examples
prev <- .10 # sets a prevalence value of 10%
prev <- 10/100 # (condition = TRUE) for 10 out of 100 individuals
is_prob(prev) # TRUE