Experiment
An experiment imposes treatments on subjects and compares their responses, supporting a cause-and-effect conclusion when treatments are assigned at random.
In an experiment the researcher actively assigns treatments rather than just observing what happens. For example, randomly assigning patients to take a new drug or a placebo and then comparing recovery rates is an experiment. Random assignment balances out other variables across the groups, which is what lets a difference in response be attributed to the treatment. Its key ideas are comparison, random assignment, and replication across many subjects.
More collecting data and study design terms, or browse the full statistics glossary.