At first glance, the laboratory experiment seems a much stronger design than the field experiment. The use of randomization allows us to rule out competing explanations, and determine that the differenence, d, was in fact due to the treatment, X. This is called internal validity. However, external validity is a real strength of field experiments, compared with lab experiments. Randomization allows us to generalize the results of our in-home lab experiment involving 150 people. Thus, external validity specifies to what times, settings, and persons can the results be generalized.
Field experiments are typically much more representative of the real-world than lab experiments.
Now, let's consider some problems in causal research design. Today's handout summarizes 8 designs. You should understand each design, and the strengths and limitations of each. Today's handout has a summary table of these threats to validity. Threats to validity.