ABSTRACT
Group comparison research involves comparing the mean scores of two or more groups of research participants on one or more dependent variables. The groups could be formed in any of three ways: The researcher could randomly assign research participants to groups, such as the experimental and control groups in a true experiment; the researcher could assess scores of members of preexisting groups, such as students in two classrooms who received different sex education interventions; or the researcher could group participants on the basis of some personal characteristic, such as gender, sexual orientation, or personality. As shown in Table. 11.1, the manner in which participants are formed into groups is one of three characteristics—manipulation of the independent variable, assignment of participants to groups, and control over extraneous situational variables—that define the three types of group comparison research: true experiments, quasiexperiments, and nonexperimental studies. This chapter begins with a brief review of some relevant statistical concepts and then discusses issues related to each of these types of research and variations on the basic designs in terms of the number of conditions of the independent variable and the number of independent variables used in the research.
