FIGURE 10.5 Hypothetical Data Showing a Relationship Between Activity Level and Drug Dosage For Five Different Levels Drug Dosage
a 1-dose group (points A and B in the figure), the data would seem to indicate that increasing the drug dose produces an increase in activity. However, a researcher comparing a 2-dose versus a 4-dose group (Points C and E) would reach exactly the opposite conclusion. Although both of two-group studies are accurate, neither provides a complete picture. In general, several groups (more than two) are necessary to obtain a good indication of the functional relationship between an independent and a dependent variable.
A two-group study also limits the options when a researcher wishes to compare a treatment group and a control group. Often, it is necessary to use several control groups to obtain a complete picture of a treatment’s effectiveness. As we noted in Chapter 9, two common controls that often are used together are a no-treatment control and a placebo control. With these two control groups, researchers can separate the real treatment effects from the placebo effects that occur simply because participants think that they are receiving treatment. However, as we noted in Chapter 3 (p. 80), there is some ethical concern regarding the use of no-treatment or placebo groups in clinical research. Rather than denying treatment to some participants, it is suggested research. Rather than denying treatment to some participants, it is suggested that an established, standard therapy be used for the control comparison (LaVaque & Rossiter, 2001).