acc
defines overall accuracy
as the probability of correspondence between a positive decision
and true condition (i.e., the proportion of correct classification
decisions or of dec_cor
cases).
acc
An object of class numeric
of length 1.
Importantly, correct decisions dec_cor
are not necessarily positive decisions dec_pos
.
Understanding or obtaining the accuracy metric acc
:
Definition:
acc
is the (non-conditional) probability:
acc = p(dec_cor) = dec_cor/N
or the base rate (or baseline probability) of a decision being correct, but not necessarily positive.
acc
values range
from 0 (no correct decision/prediction)
to 1 (perfect decision/prediction).
Computation: acc
can be computed in several ways:
(a) from prob
: acc = (prev x sens) + [(1 - prev) x spec]
(b) from freq
: acc = dec_cor/N = (hi + cr)/(hi + mi + fa + cr)
(c) as complement of the error rate err
: acc = 1 - err
When frequencies in freq
are not rounded, (b) coincides with (a) and (c).
Perspective:
acc
classifies a population of N
individuals
by accuracy/correspondence (acc = dec_cor/N
).
acc
is the "by accuracy" or "by correspondence" counterpart
to prev
(which adopts a "by condition" perspective) and
to ppod
(which adopts a "by decision" perspective).
Alternative names: base rate of correct decisions, non-erroneous cases
In terms of frequencies,
acc
is the ratio of
dec_cor
(i.e., hi + cr
)
divided by N
(i.e.,
hi + mi
+ fa + cr
):
acc = dec_cor/N = (hi + cr)/(hi + mi + fa + cr)
Dependencies:
acc
is a feature of both the environment (true condition) and
of the decision process or diagnostic procedure. It reflects the
correspondence of decisions to conditions.
See accu
for other accuracy metrics
and several possible interpretations of accuracy.
Consult Wikipedia:Accuracy_and_precision for additional information.
comp_acc
computes accuracy from probabilities;
accu
lists all accuracy metrics;
comp_accu_prob
computes exact accuracy metrics from probabilities;
comp_accu_freq
computes accuracy metrics from frequencies;
comp_sens
and comp_PPV
compute related probabilities;
is_extreme_prob_set
verifies extreme cases;
comp_complement
computes a probability's complement;
is_complement
verifies probability complements;
comp_prob
computes current probability information;
prob
contains current probability information;
is_prob
verifies probabilities.
Other probabilities:
FDR
,
FOR
,
NPV
,
PPV
,
err
,
fart
,
mirt
,
ppod
,
prev
,
sens
,
spec
Other metrics:
accu
,
comp_accu_freq()
,
comp_accu_prob()
,
comp_acc()
,
comp_err()
,
err
acc <- .50 # sets a rate of correct decisions of 50%
acc <- 50/100 # (dec_cor) for 50 out of 100 individuals
is_prob(acc) # TRUE
#> [1] TRUE