ABSTRACT
The three previous chapters discussed the design and analyses of single factor studies, where there was only one independent variable. However, it is uncommon to find in current literature the case where only one independent variable is present. In this chapter we introduce a second between groups independent variable, discuss the advantages of having more than one independent variable, and demonstrate how these designs (complex designs) are analyzed and interpreted. In chapter 18, we continue our discussion on complex designs by introducing a repeated measures independent variable as the second independent variable, creating a mixed design. Remember, that in chapter 12, we discussed the three general design classifications (between groups, within subjects, and mixed) and noted that they determine the specific statistics to use in data analysis. Although we are adding a second independent variable in the current chapter, the designs are still between groups because both independent variables are between groups independent variables. However, most of the experimental designs in chapter 18 are mixed designs, which by definition have at least two independent variables, one between groups and one within subjects (repeated measures). These mixed, twofactor designs are often those with a pretest and a posttest (within subjects) and with experimental and control groups (between groups).
