# comp_PPV

##### Compute a decision's positive predictive value (PPV) from probabilities.

`comp_PPV`

computes the positive predictive value `PPV`

from 3 essential probabilities
`prev`

, `sens`

, and `spec`

.

##### Usage

`comp_PPV(prev, sens, spec)`

##### Arguments

- prev
The condition's prevalence

`prev`

(i.e., the probability of condition being`TRUE`

).- sens
The decision's sensitivity

`sens`

(i.e., the conditional probability of a positive decision provided that the condition is`TRUE`

).- spec
The decision's specificity value

`spec`

(i.e., the conditional probability of a negative decision provided that the condition is`FALSE`

).

##### Details

`comp_PPV`

uses probabilities (not frequencies)
and does not round results.

##### Value

The positive predictive value `PPV`

as a probability.
A warning is provided for NaN values.

##### See Also

`comp_sens`

and `comp_NPV`

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 functions computing probabilities: `comp_FDR`

,
`comp_FOR`

, `comp_NPV`

,
`comp_accu_freq`

,
`comp_accu_prob`

, `comp_acc`

,
`comp_comp_pair`

,
`comp_complement`

,
`comp_complete_prob_set`

,
`comp_err`

, `comp_fart`

,
`comp_mirt`

, `comp_ppod`

,
`comp_prob_freq`

, `comp_prob`

,
`comp_sens`

, `comp_spec`

##### Examples

```
# NOT RUN {
# (1) Ways to work:
comp_PPV(.50, .500, .500) # => PPV = 0.5
comp_PPV(.50, .333, .666) # => PPV = 0.499
# (2) Watch out for vectors:
prev <- seq(0, 1, .1)
comp_PPV(prev, .5, .5) # => without NaN values
comp_PPV(prev, 0, 1) # => with NaN values
# (3) Watch out for extreme values:
comp_PPV(prev = 1, sens = 0, spec = .5) # => NaN, only mi: hi = 0 and fa = 0: PPV = 0/0 = NaN
is_extreme_prob_set(prev = 1, sens = 0, spec = .5) # => verifies extreme cases
comp_PPV(prev = 0, sens = .5, spec = 1) # => NaN, only cr: hi = 0 and fa = 0: PPV = 0/0 = NaN
is_extreme_prob_set(prev = 0, sens = .5, spec = 1) # => verifies extreme cases
comp_PPV(prev = .5, sens = 0, spec = 1) # => NaN, only cr: hi = 0 and fa = 0: PPV = 0/0 = NaN
is_extreme_prob_set(prev = .5, sens = 0, spec = 1) # => verifies extreme cases
# }
```

*Documentation reproduced from package riskyr, version 0.2.0, License: GPL-2 | GPL-3*