In Search of Causality: True Experiments

1. A true experiment provides the best test of whether manipulation of an independent variable causes changes in a dependent variable.
2. The internal validity of an experiment is defined as the extent to which the systematic manipulation of one or more independent variables produces the predicted or hypothesized effect on the dependent variable.
3. The goal is to design an internally valid experiment that will allow the researcher to establish causal relationships among the key variables under study.
4. Sample generalizability, replication of findings, and real-world impact of the results (ecological validity) increase external validity of experiments.
5. We should exercise caution (in the spirit of the scientific method) in drawing any causal conclusion that an independent variable caused a change in a dependent variable.