1. Causal research design uses experimentation to determine causal relationships. Experiments manipulate an independent variable to measure its effect on a dependent variable. 2. There are different types of experimental designs that vary in their ability to establish causality depending on whether they include control groups, random assignment, and pre-testing. More rigorous designs like the pretest-posttest control group design better control for extraneous variables. 3. Extraneous variables like history, maturation, testing, instrumentation, and mortality can influence outcomes and must be controlled through randomization, matching, statistical controls or design features.