Glossary
independent variable
The independent variable is the one condition an experimenter changes on purpose — the input a hypothesis varies to see what follows.
The independent variable is the condition an experimenter changes on purpose. It is the input: the sanitizer concentration in a plate trial, the drug dose in a trial of a drug, the temperature in a trial of germination. Everything the experimenter controls and holds steady is a constant; everything that changes because of the independent variable is the dependent one.
The name is a memory hook, not a description of independence. The independent variable does not depend on anything else in the experiment — it is set, not measured. The dependent variable depends on it: measure the colony count and the count depends on the concentration.
A useful test for an item is to find the word changed, varied, compared or different in the stem. The condition the experimenter varied is the independent variable; the outcome that was measured afterwards is the dependent one. If a study instead compares groups that already differ, with nothing varied, it is observational and the same vocabulary does not apply cleanly.
Taught in
Related terms
- dependent variable — The dependent variable is what an experiment measures — the outcome that changes in response to the independent variable.
- hypothesis — A hypothesis is a testable, falsifiable statement that predicts what an experiment will show — the proposed answer a controlled test is designed to check.
Source: The biology guide in this course: its genetics definitions follow the National Human Genome Research Institute's Talking Glossary of Genomic and Genetic Terms, and its process descriptions follow the US National Cancer Institute's SEER Training Modules. Both are US federal government material, not subject to copyright in the United States. The microbiology entries — the bacterial cell, the Gram stain and the chain of infection — were written for this course from the infection-control guidance the biology guide's own source list names (US Centers for Disease Control and Prevention), which the genetics glossary does not cover. The definitions above are written for this course in our own words. (NHGRI Talking Glossary accessed 2026-10-26; definitions written 2026-10-27; the CDC basis for the microbiology entries — Principles of Epidemiology in Public Health Practice, third edition — accessed 2026-10-28, the date the biology guide's own source list records)