medtests.net · Glossary

Glossary: Understanding test methodology and results

What does a positive screening mean? How well does a questionnaire measure at all? And why does the frequency of a condition change what a result tells you? This glossary explains the most important terms in test methodology in calm, clear language. It is not a test and does not provide an evaluation. It helps you understand the results of the self-tests on medtests.net.

Methodology with sources clear limits

What this glossary is for

Almost every self-test gives you a result that needs explanation. A value above a cutoff does not mean that a condition is definitely present, and a value below it does not rule anything out. So you do not have to read these statements again on every test page while still understanding what they are based on, we collect the underlying terms here in one place. The articles are organized around four user questions rather than alphabetically because this makes the methodology easier to follow.

How do questionnaires work?

Many self-tests consist of statements that you rate on a scale. This term explains how this response format works and what it tells you about a result.

Likert scale Why many questionnaires use response options from "strongly disagree" to "strongly agree," and what the difference is between a single item and a scale. Percentile How a percentile rank compares an individual result with a reference group.

How well does a test measure?

Whether you can rely on a test result depends on two questions. Does the test measure the right thing, and does it measure reliably? These terms explain what those questions mean.

Validity The question of whether a test measures what it is supposed to measure, and why validity is always tied to a specific purpose and context. Reliability How reliably a test measures the same thing when what is being measured has not changed, and why a test can also reliably measure the wrong thing.

What does a screening result mean?

A self-test is usually a screening. These terms explain what a positive or negative result really tells you and where the limits are.

Sensitivity and specificity Two measures of how well a test identifies people with a condition and correctly identifies people without it, explained with a 2x2 table. Screening test The difference between an initial screening and a diagnosis, and why a result always remains an indication, not a judgment.

Why does the frequency of a condition change what a result tells you?

How informative a result is also depends on how common a condition is. This term explains the relationship.

Prevalence How often a condition occurs in a group, and why the same test can provide different amounts of information when a condition is rare or common. Positive predictive value How informative a positive result is and why prevalence plays a major role.

Note

This glossary explains methodology and does not replace medical, psychotherapeutic, or diagnostic evaluation. The main sources for each term are listed on the respective page. You can find an overview of the standard sources under Sources. Created by the medtests editorial team. Last updated: July 12, 2026. Editorially reviewed, without external expert review.