population of all adults, then it is necessary for adults of all ages, genders, and ethnic backgrounds to be included in the study.
population: in a research study, the larger group of individuals to which the results can be generalized
Researchers use a variety of means for selecting participants. The best is some form of random sampling. You might choose every tenth person in the college directory, or every fourth person admitted to the ward for treatment of schizophrenia, for example. When the selection is not random—that is, every person is not equally likely to be chosen—then bias can appear.
Figure 3.7 How Do You Perform an Experiment?
Putting Participants in Groups
After the participants have been randomly selected from the larger population under study, they can then be randomly assigned to experimental and control groups. This ensures that the groups are equal before the experiment begins. Randomization controls for both known and unknown potentially confounding variables. Randomization leaves solely to chance the assignment of participants to a group. In this way, any differences—even unknown or unsuspected differences—will also be nullified by being randomly distributed between the two groups.
In medical and psychological treatment research, the gold standard is considered to be the randomized control trial (RCT). RCTs assign individuals randomly to the treatments being studied. For example, in a recent study of the effectiveness of certain stress reduction strategies, Melissa Polusny and her colleagues (2015) randomly assigned veterans at the Minneapolis Veterans Affairs Medical Center to one of two treatments. The first was a mindfulness-based stress reduction procedure. The comparison treatment centered on having the therapy focus on the current problems in the person’s life. In this study, mindfulness resulted in a greater reduction in the PTSD symptoms compared with the current problems procedure.
In 1995, identical twin brothers David (left) and Steven (right) Elmore took part in E. Fuller Torrey’s classic study. David is mentally healthy, and Steven has schizophrenia. The study found that Steven’s brain has less tissue and larger ventricles than David’s.
Joe McNally/Contributor/Hulton Archive/Getty Images
randomization: in an experiment, selection of participants solely by chance to either the experimental group or the control group
randomized control trial (RCT): an experimental procedure in which participants in the study are randomly assigned to the treatment group or the control group for the independent variable being studied
match subjects design: a design type in psychopathology research in which the closer a scientist can match individuals in the experimental and control groups, the stronger the logic of the design
Much of the early research involving clinical disorders was based on observation and interviews. With the advent of psychological testing and more advanced neuroscience techniques, greater insight has been gained in the structures and mechanisms involved in mental health and illness. Since mental illness cannot be studied in a traditional experimental manner, new methodologies and statistical techniques for comparing genetic, physiological, cognitive, emotional, gender, and stress factors are being developed.
One important design type in psychopathology research is a match subjects design. The closer a scientist can match individuals in the experimental and control groups, the stronger the logic of the design. A researcher cannot randomly assign individuals to control and experimental groups if the experimental group is composed of individuals with a specific disorder and the control group is composed of individuals without that disorder. Therefore, an alternative method other than random assignment must be used to ensure that the two groups are similar on characteristics not under study. Some important variables include education level, socioeconomic status (SES), general health, types of medications used, age, gender, and others related to the specific question being asked in the research. Thus, the general task is to ensure that the participants in the study are like one another except for having a mental illness. For example, when Tom Borkovec and his colleagues (Borkovec & Ruscio, 2001) sought to determine if cognitive behavioral therapy was effective in treating generalized anxiety disorder (GAD) as compared with other treatments, it was important that those with anxiety were matched in terms of age, gender, income, education level, and other such variables in terms of the experimental conditions.
The strongest version of matching is to use identical twins. The situation in which one twin has a particular disorder and the other does not helps to focus on the critical variables. One classic study involving twins was performed by E. Fuller Torrey (1994) and his colleagues in the 1990s. They studied individuals who developed schizophrenia or bipolar disorder (manic depression). Twins who lived together were matched in terms of such factors as genetics, family history, SES, and a number of others. However, twins are not always available, and thus researchers need to match those with a disorder and those without. I’ll discuss the use of twins in psychological research at greater length in the Behavioral Genetics section later in this chapter.
Designing and Structuring the Experimental Study
Science is a way of asking questions about the world. The quality of the answers we receive is influenced by several factors, one of the most important being the experimental design that we use. Somewhat like a blueprint, the experimental design directs the procedures and gives form to the experiment. In essence, an experimental design is a plan for how a study is to be structured.
In an outline form, a design tells us what will be done to whom and when. To be evaluated favorably, a design must perform two related functions. First, it must provide a logical structure that enables us to pinpoint the effects of the IV on the DV and thus answer our research questions. Second, it must help us rule out confounds as an alternative explanation for our findings.
Imagine a study in which a clinical psychologist was interested in determining if teaching children with autism to look at a person’s face would increase their interaction with others. Thus, the question asked would be whether looking at a face (IV) results in the participant interacting more with others (DV). After the subject was taught to look at a face, he or she could be placed in situations in which other individuals were present. The researcher could measure the number of interactions in which the child engaged.
If we were to diagram the design of this study, it would be as follows:
Select the group → Teach facial focus → Measure number of interactions
If we performed the experiment with just a single group, what could we conclude? We could determine if our participants had a certain number of interactions. However, this would not help us determine if this was related to the facial focus procedure. Such a design would not be much help in pinpointing the effect of the IV on the DV, nor would it rule out confounds.
A stronger design would use a control group. This design would appear as follows:
Experimental group → Teach facial focus → Measure number of interactions
Control group → No treatment → Measure number of interactions
Since the control group had not received the treatment, we would have stronger evidence that the treatment
