1	a typical experiment prototype of a controlled laboratory investigation
2	In the most typical experiment Subjects are randomly assigned to a “treatment” or “control” group. The “treatment” group is exposed to the experimental stimulus. The “control” group is not exposed to the experimental stimulus The researcher measures any resulting differences between the treatment and control group
3	Example 1: treatment group versus control group RQ: Does caffeine consumption increase physical stamina? Independent variable: caffeine consumption versus no caffeine consumption Dependent variable: physical stamina as measured by the total distance jogged on a treadmill
4	Random assignment Random assignment produces equivalent groups for comparison purposes 200 volunteers are randomly assigned to a treatment group or control group
5	Operationalization of the independent variable treatment group Consumes 12 oz. (500 milligrams) of coffee just before jogging on a treadmill control group Consumes 12 oz. Of decaffeinated coffee just before jogging on a treadmill
6	Measurement of the dependent variable The total distance of each jogger is measured by the treadmill’s counter to the nearest 1/10 mile. There is no time limit. Two observers watch to ensure the joggers are jogging (8-10 minute pace), not walking, until they stop. The average distance of the joggers in the treatment group is then compared with the average distance of joggers in the control group.
7	Example 2: comparison groups RQ: Do dog owners report greater relationship satisfaction than cat owners? Independent variable: pet ownership, e.g., dogs owners versus cat owners Dependent variable: relationship satisfaction, as measured by the “Dyadic Adjustment Scale.”
8	Non-random assignment Some experiments rely on “intact” or “self-selected” groups People already own their pets. They can’t be randomly assigned to own one pet or another
9	Operationalization of the independent variable 91 dog owners are selected using a “mall intercept” technique The dog owners do not own a cat or any other pets. 103 cat owners are selected using a “mall intercept” technique The cat owners do not own a dog or any other pets.
10	Measurement of the dependent variable All of the respondents are asked to complete the “Dyadic Adjustment Scale” a paper-pencil survey that asks respondents to rate the quality of their relationship with a significant other. The average ratings of the dog owners are then compared with the average ratings of the cat owners to see if there is a significant difference.