Experimental Method The key features are controlled methods and the random allocation of participants into controlled and experimental groups. In an experiment, an independent variable (the cause) is manipulated and the dependent variable (the effect) is measured; any extraneous variables are controlled.

True experiments have four elements: manipulation, control , random assignment, and random selection. The most important of these elements are manipulation and control. Manipulation means that something is purposefully changed by the researcher in the environment.

Characteristics of a Well-Designed Experiment

• Control. Control refers to steps taken to reduce the effects of extraneous variables (i.e., variables other than the independent variable and the dependent variable).
• Randomization.
• Replication.

Internal validity can be assessed based on whether extraneous (i.e. unwanted) variables that could also affect results are successfully controlled or eliminated; the greater the control of such variables, the greater the confidence that a cause and effect relevant to the construct being investigated can be found.

A valid causal inference may be made when three criteria are satisfied: the “cause” precedes the “effect” in time (temporal precedence), the “cause” and the “effect” tend to occur together (covariation), and. there are no plausible alternative explanations for the observed covariation (nonspuriousness).

Internal Validity refers to those factors that are the reason for affecting the dependent variable. Construct Validity refers to the type in which the construct of the test is involved in predicting the relationship for the dependent type of variable.

Construct validity means the test measures the skills/abilities that should be measured. Content validity means the test measures appropriate content.