Experiment - At least one independent variable is manipulated.

Experimental Design - the structure by which variables are positioned or arranged in an experiment.

Experimental Validity Threats Internal History Maturation Testing Instrumentation Statistical regression Selection Mortality	External Interaction effect of testing Interaction of selection and treatment Reactive effects of arrangements Multiple treatment interference
Construct Inadequate explication Mono-operation bias Mono-method bias Hypothesis guessing Confounding constructs with levels	Statistical Conclusion Low statistical power Violated assumptions Fishing and error rate Reliability of measures
Experimental designs Posttest-only control group design Pretest-posttest control group design Solomon four-group design Factorial designs Repeated measures designs

Random assignment for internal validity
Random selection for external validity