What is experimental design?
Experimental design refers to a plan for assigning experimental units to treatment conditions. A good experimental design serves the following three purposes:
#1 Causation -enables experimenter to make causal inferences about the relationship between independent variables and a dependent variable.
#2 Control -enables the experimenter to rule out alternative explanations due to the confounding effects of extraneous variables (i.e., variables other than the independent variables).
#3 Variability-reduces variability within treatment conditions (so it's easier to detect differences in treatment outcomes).
#2 Control -enables the experimenter to rule out alternative explanations due to the confounding effects of extraneous variables (i.e., variables other than the independent variables).
#3 Variability-reduces variability within treatment conditions (so it's easier to detect differences in treatment outcomes).
When and why do we use experimental design?
We use experimental design when we want to use the most "rigorous" of all research designs. The reason why we do so is because experimental design is considered the "gold standard" against which all other designs are judged. A well implemented experimental design means the strongest design with respect to internal validity. When you want to determine whether a treatment causes an outcome to occur, then you want to have strong internal validity.
Definitions: Internal validity refers to how well an experiment is done, especially whether it avoids confounding. (Confounding means more than one possible independent variable [cause] acting at the same time.)
