The primary disadvantage of a two-group design is that it provides relatively little information. With only two groups, a researcher obtains only two real data points for comparison. Although two data points are sufficient to establish a difference, they often are not sufficient to provide a complete or detailed picture of the full relationship between an independent and a dependent variable. Figure 10.5 shows a hypothetical relationship between dosage levels for a drug (independent variable). Notice that the complete set of five data points, representing five different drug doses, gives a good picture of how drug dosage affects. Now, consider the limited data that would be available if the researcher had used only two different drug doses. If, for example, the researcher had used only a 0-dose and