Glossary
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.
A hypothesis is a testable, falsifiable statement that predicts the outcome of an experiment. If the sanitizer is present, then fewer colonies will grow is a hypothesis: it names a change and a predicted result, and a plate count can prove it wrong.
Two words carry the definition. Testable means the prediction can be checked with an observation or a measurement, not just argued about. Falsifiable means some possible result would count against it — a claim that cannot fail is not a hypothesis, whatever else it may be.
A hypothesis is not a question (does sanitizer kill bacteria? is the question it answers), and it is not a guess with no prediction attached. It is also not the same thing as a theory: a theory is a broad explanation supported by a body of evidence and still open to test, which is the opposite of the everyday use of the word.
In a controlled experiment the hypothesis decides the variables. The condition the investigator changes is the independent variable, the measurement that answers the prediction is the dependent variable, and the control group shows what happens without the treatment.
Taught in
Related terms
- independent variable — The independent variable is the one condition an experimenter changes on purpose — the input a hypothesis varies to see what follows.
- dependent variable — The dependent variable is what an experiment measures — the outcome that changes in response to the independent variable.
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)