Compute sensitivity, specificity, PPV, NPV, likelihood ratios, DOR, and Shannon entropy from a 2×2 table. Wilson or Clopper-Pearson CIs. Data never leaves your browser.
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Enter the four cells of the 2×2 contingency table.
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Sensitivity and specificity are stable properties of the test, but PPV and NPV shift dramatically with disease prevalence. A test with 95% sensitivity and 95% specificity has a PPV of only 16% at 1% prevalence. Always report the prevalence alongside PPV/NPV.
Wilson score intervals have better coverage properties and are never degenerate (e.g., [0, 0] when the proportion is 0). Use Clopper-Pearson exact CIs only when strict coverage guarantees are required, such as regulatory submissions.
When any cell of the 2×2 table is zero, likelihood ratios and DOR become undefined. The Haldane-Anscombe correction (adding 0.5 to all cells) produces finite estimates with valid CIs. This is standard in meta-analysis.
LR+ and LR− are independent of prevalence, making them transferable across clinical settings. An LR+ > 10 or LR− < 0.1 provides strong diagnostic evidence regardless of the population.
Diagnostic accuracy metrics are computed from a 2×2 contingency table (TP, FP, FN, TN). Sensitivity, specificity, PPV, and NPV use standard proportion formulas with Wilson score or Clopper-Pearson exact confidence intervals. Likelihood ratios and DOR use log-scale CIs. Shannon entropy information gain is computed as the reduction in binary entropy from pretest to expected post-test uncertainty. The Haldane-Anscombe correction (adding 0.5 to all cells) is applied when any cell is zero. All calculations run client-side in the browser.
Published 2026-04-05. Calculations support planning and documentation; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience Diagnostic Test Calculator. ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/diagnostic-test-calculator
Wilson EB. Probable inference, the law of succession, and statistical inference. J Am Stat Assoc. 1927;22(158):209-212. doi:10.1080/01621459.1927.10502953
Diagnostic test evaluation centers on the 2×2 table — the cross-classification of a reference standard (gold standard) and the index test. From this table, we compute:
• Sensitivity = TP / (TP + FN) — detection rate among the diseased • Specificity = TN / (FP + TN) — exclusion rate among the non-diseased • PPV = TP / (TP + FP) — precision of a positive result • NPV = TN / (FN + TN) — precision of a negative result • LR+ = Sens / (1 − Spec) — how much a positive test increases disease odds • LR− = (1 − Sens) / Spec — how much a negative test decreases disease odds
Sensitivity and specificity are properties of the test (stable across populations). PPV and NPV depend on prevalence — the same test can have a PPV of 95% at 50% prevalence and 30% at 2% prevalence.
Shannon entropy provides a principled measure of diagnostic uncertainty. For a binary outcome with probability p:
Maximum uncertainty (1 bit) occurs at p = 0.5. The information gain from a test is:
where E[H(posttest)] = P(T+) · H(posttest|T+) + P(T−) · H(posttest|T−). A test with high information gain dramatically reduces uncertainty regardless of the result. This metric is more nuanced than accuracy — a test can have high accuracy in low-prevalence settings while providing almost zero information.
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