Source: https://guthlabs.ai/docs/instruments/sensitivity-specificity-ppv-npv-calculator/
instrument / verified-clean
# Sensitivity/Specificity/PPV/NPV Calculator
The current ledger marks this instrument verified clean within the source-bound verification corpus.
Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**
## Inspectable records
[01**Overview**Purpose and lifecycle]()[02**Mechanism**Method and assumptions]()[03**Implementation**Binding and validation]()[04**Qualification**Evidence and errata]()
## Ledger state
The current ledger marks this instrument verified clean within the source-bound verification corpus.
**Area**: Biology, Medicine & Pharmacology (educational estimates only — every panel labeled not-medical-advice)
**Tranche**: tranche-5
**Evidence ID**: t5-175
**Ledger rows**: 1
No ledger note is attached.
## Review findings
The core five listed expressions are standard under the stated unit assumptions. The specification needs an explicit input mode, denominator/error policy, LR− formula, and positive/negative post-test probability formulas before it can be treated as complete.
### Formula and scope findings
- The listed formulas correctly define sensitivity, specificity, PPV, NPV, and LR+ for a diagnostic 2x2 table, assuming all denominators are nonzero.
- The output claims likelihood ratios plural, but only LR+ is specified; the standard LR− formula is missing: LR−=(1−Sensitivity)/Specificity.
- Post-test probability formulas are missing. For a positive result, post-test probability equals PPV when calculated from the same table; from prevalence, sensitivity, and specificity it is (prevalence×sensitivity)/[(prevalence×sensitivity)+((1−prevalence)×(1−specificity))]. For a negative result, it is NPV, calculated from prevalence as ((1−prevalence)×specificity)/[((1−prevalence)×specificity)+(prevalence×(1−sensitivity))].
- The input specification is ambiguous because it permits either TP/FP/FN/TN counts or prevalence+sensitivity+specificity, but does not define how outputs are calculated or labeled for each input mode.
### Unit assumptions
- TP, FP, FN, and TN are nonnegative integer counts of mutually exclusive and collectively exhaustive outcomes.
- Sensitivity, specificity, and prevalence are proportions from 0 to 1; percentage inputs such as 90% must be converted to 0.90 before calculation.
- All four 2x2 cells must refer to the same population, test threshold, and time frame.
- For count inputs, prevalence is assumed to be (TP+FN)/(TP+FP+FN+TN).
- Ratios and probabilities are dimensionless; counts must not be mixed with percentages or fractions without explicit conversion.
## Boundary hardening
**BREAK_CLAIMED** · SELF_FLAGGED
The specification permits zero-count tables and ambiguous prevalence input without stating denominator guards or an explicit percent-versus-fraction convention. Zero denominators produce undefined sensitivity, PPV, and LR+, while interpreting prevalence 5 as a fraction produces invalid probabilities above 1.
## Errata and corrections
No applied erratum is attached to this unique-name record.
## Inspectable example
4 review vectors are recorded. One source-bound sample is shown below.
````
{
"inputs": {
"TP": 80,
"FP": 100,
"FN": 20,
"TN": 900
},
"expected_outputs": {
"sensitivity": 0.8,
"specificity": 0.9,
"PPV": 0.4444444444,
"NPV": 0.9782608696,
"LR+": 8,
"LR-": 0.2222222222,
"prevalence": 0.0909090909,
"post_test_probability_positive": 0.4444444444,
"post_test_probability_negative": 0.9782608696
},
"working": "Total=80+100+20+900=1100. Sensitivity=80/(80+20)=80/100=0.80. Specificity=900/(900+100)=900/1000=0.90. PPV=80/(80+100)=80/180=0.4444444444. NPV=900/(900+20)=900/920=0.9782608696. LR+=0.80/(1−0.90)=0.80/0.10=8. LR−=(1−0.80)/0.90=0.20/0.90=0.2222222222. Prevalence=(80+20)/1100=100/1100=0.0909090909. Positive post-test probability=PPV=0.4444444444. Negative post-test probability=NPV=0.9782608696."
}
````
## Related workflows
No source-defined multi-instrument workflow membership is recorded.
## Sources and evidence
These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.
- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`
- `evidence-tranche5/tranche5-results.json`
- `BOUNDARY_HAZARD_CATALOG.json`