[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Epidemiology](https://durgical.com/en/epidemiology/) › Diagnostic tests

# Diagnostic tests

Sensitivity, specificity, predictive values, likelihood ratios, the ROC curve and pre- and post-test probability.

15 pages

## Measure

- [**Agreement and the kappa statistic** Kappa measures how much two observers agree beyond what they would agree on by pure chance](https://durgical.com/en/epidemiology/agreement-and-the-kappa-statistic/)
- [**Agreement for continuous measures: ICC and Bland-Altman** Two devices can correlate almost perfectly and still not give the same values](https://durgical.com/en/epidemiology/agreement-for-continuous-measures-icc-and-bland-altman/)
- [**Likelihood ratios** How much more likely a result is in someone with the disease than in someone without; it shows…](https://durgical.com/en/epidemiology/likelihood-ratios/)
- [**Overall accuracy and Youden index** Accuracy counts correct results over the total; the Youden index adds sensitivity and…](https://durgical.com/en/epidemiology/overall-accuracy-and-youden-index/)
- [**Positive and negative predictive values** If the test is positive (or negative), how likely the person is to have (or not have) the…](https://durgical.com/en/epidemiology/positive-and-negative-predictive-values/)
- [**Sensitivity** Of all the people who have the disease, the share the test correctly calls positive](https://durgical.com/en/epidemiology/sensitivity/)
- [**Specificity** Of all the healthy people, the share the test correctly calls negative](https://durgical.com/en/epidemiology/specificity/)

## Concept

- [**Choosing a cutoff: sensitivity vs specificity** Moving the value that separates positive from negative trades false negatives for false…](https://durgical.com/en/epidemiology/choosing-a-cutoff-sensitivity-vs-specificity/)
- [**How prevalence changes predictive values** The same test's positives are right more often where the disease is common and less often where…](https://durgical.com/en/epidemiology/how-prevalence-changes-predictive-values/)
- [**Measurement variation** Measuring the same thing twice almost never gives the same result: the person changes, the…](https://durgical.com/en/epidemiology/measurement-variation/)
- [**Pre-test and post-test probability** Suspicion before the test, adjusted by the result, gives the probability of disease after the…](https://durgical.com/en/epidemiology/pre-test-and-post-test-probability/)
- [**Reference standard (gold standard)** The best available way to know who has the disease; every other test's performance is measured…](https://durgical.com/en/epidemiology/reference-standard/)
- [**ROC curve** A plot of sensitivity against 1 − specificity across all cutoffs; its area sums up how well the…](https://durgical.com/en/epidemiology/roc-curve/)
- [**Serial and parallel testing** Combining two tests changes performance: serial testing raises specificity, parallel testing…](https://durgical.com/en/epidemiology/serial-and-parallel-testing/)
- [**Validity and reliability** Validity is measuring the true value; reliability is getting the same value when the measurement…](https://durgical.com/en/epidemiology/validity-and-reliability/)

## A to Z

- [A](https://durgical.com/en/epidemiology/a-z/a/)
- [B](https://durgical.com/en/epidemiology/a-z/b/)
- [C](https://durgical.com/en/epidemiology/a-z/c/)
- [D](https://durgical.com/en/epidemiology/a-z/d/)
- [E](https://durgical.com/en/epidemiology/a-z/e/)
- [F](https://durgical.com/en/epidemiology/a-z/f/)
- [G](https://durgical.com/en/epidemiology/a-z/g/)
- [H](https://durgical.com/en/epidemiology/a-z/h/)
- [I](https://durgical.com/en/epidemiology/a-z/i/)
- [K](https://durgical.com/en/epidemiology/a-z/k/)
- [L](https://durgical.com/en/epidemiology/a-z/l/)
- [M](https://durgical.com/en/epidemiology/a-z/m/)
- [N](https://durgical.com/en/epidemiology/a-z/n/)
- [O](https://durgical.com/en/epidemiology/a-z/o/)
- [P](https://durgical.com/en/epidemiology/a-z/p/)
- [Q](https://durgical.com/en/epidemiology/a-z/q/)
- [R](https://durgical.com/en/epidemiology/a-z/r/)
- [S](https://durgical.com/en/epidemiology/a-z/s/)
- [T](https://durgical.com/en/epidemiology/a-z/t/)
- [U](https://durgical.com/en/epidemiology/a-z/u/)
- [V](https://durgical.com/en/epidemiology/a-z/v/)
- [W](https://durgical.com/en/epidemiology/a-z/w/)
- [Y](https://durgical.com/en/epidemiology/a-z/y/)

[← Epidemiology, biostatistics and public health](https://durgical.com/en/epidemiology/)

Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/epidemiology/areas/diagnostic/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/epidemiology/areas/diagnostic/