An experiment deliberately imposes a treatment on a group of objects or subjects in the interest of observing the response.
Research design is a plan for collecting and utilizing data so that desired information can be obtained with sufficient precision or so that an hypothesis can be tested properly.
There are several different types of research design in psychology including:
See the boxes in the left column for information about these types of research design.
Populations & sampling: a population is any set of people or research subjects having a common observable characteristic. A sample consists of a subset of the population.
Reliability: A test is reliable when it yields consistent results.
Validity: A test is valid when it measures what it's supposed to.