In addition to being able to analyze an experiment with one Independent Variable (IV), the ANOVA can be used for factorial designs (or designs which employ more than one IV). Note that, in this context, an IV is often referred to as a factor. The factorial design is very popular in the social sciences. It has a few advantages over single variable designs. The most important of these is that it can provide some unique and relevant information about how variables interact or combine in the effect they have on the DV.Let's look at these design issues in more detail with a concrete example and then consider the unique information that this design provides.
Our example involves the effects of maternal consumption of ethanol on the behavior of the offspring of rats. The human literature had shown that children diagnosed with Fetal Alcohol Syndrome (FAS) were more active and impulsive than children not receiving this diagnosis. They also seemed to have a more difficult time controlling themselves (i.e. self restraint). These problems typically become
less severe as the child ages.
The human literature is difficult to interpret however, because questions remain as to the cause and effect relationships involved. Were the behavioral abnormalities observed in the children with FAS due to the fact that their mothers consumed alcohol while they were pregnant? Or, were the abnormalities observed due to nutritional factors (since the diet of an alcoholic is typically not wholesome & well balanced)? Another possible causal factor of the abnormalities observed is spousal abuse.
Ethically, we cannot conduct the experiments necessary to determine the causal relations involved in humans. Thus, the experiment that will serve as our example employed rats as subjects (based on Riley, Lockrey & Shapiro, 1979). Earlier literature had demonstrated that rats can be used as an animal model of FAS. Offspring of rodents given alcohol when pregnant show similar morphological and behavioral changes to that observed in humans.
So, we will have two IVs or factors and each will have two levels (or possible values). The table below illustrates the design. Note that EDC refers to Ethanol Derived Calories .