The dependent variable is the outcome that an experimenter measures. It is expected to change as a result of manipulations of the independent variable.

In a study of sleep and memory, the independent variable might be the amount of sleep allowed; the dependent variable would be performance on a memory test the next day. In a drug trial, the independent variable is the dose or presence of the drug; the dependent variable might be symptom severity, reaction time, or brain activity. Clear operational definitions turn abstract concepts into measurable quantities so that results can be compared across studies.

A well-designed experiment holds other factors constant so that changes in the dependent variable can be attributed to the independent variable rather than to confounds. Multiple dependent variables are sometimes recorded to capture different facets of the same phenomenon. Statistical analysis then determines whether the observed differences are larger than would be expected by chance.

The dependent variable is the answer the experiment is designed to obtain. Everything else is arranged to make that answer trustworthy.