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when a participant’s response is influenced more by the research setting than by the IV. For example, a study might examine the effects of a drug as compared with exercise on reducing hyperactivity in adults. Many participants might believe the drug to be most effective, especially if the drug was given by a mental health professional and the exercise by a non–mental health professional. Those who received the drug might look for signs the drug was reducing hyperactivity. They might then pay more attention to the task used as the DV. If demand characteristics play an important role in the experiment, then they pose a significant threat to internal validity and offer an alternative explanation for understanding the influence of the IV.

      demand characteristics: bias that occurs when a participant’s response is influenced more by the research setting than by the independent variable (IV)

      placebo effect: the phenomenon that some people show psychological and physiological changes just from the suggestion that a change will take place

      experimenter effects: bias that occurs due to the experimenter’s expectations

      double-blind experiment: research procedure in which participants do not know whether they are in the experimental group or the control (placebo) group, and the researchers involved in the study also do not know which participants are in which group

      blind controls: research participants who do not know whether they are in the experimental group or the control (placebo) group

      A related phenomenon is referred to as the placebo effect. The term placebo comes from the Latin verb placere, which means “to please.” It refers to the phenomenon that some people show psychological and physiological changes just from the suggestion that a change will take place. How might this occur in a treatment study to reduce anxiety?

      Experimenters also have expectations. For example, knowing that one set of subjects has been assigned to one condition rather than another could result in those participants being treated differently. Such situations are referred to as experimenter effects.

      To control for the placebo effect in research as well as experimenter effects, various procedures have been used. One is to use a control group that receives either no treatment or a treatment previously shown to be ineffective for the particular disorder under study. In medical research, it is common to give a “sugar pill” that looks exactly like the medicine with the active ingredient. In psychotherapy research, a control group could be given relaxation training, which has been shown not to be effective on its own for mental disorders.

      A more powerful control is to use a double-blind experiment in which the experimental group is divided into two groups. One group is given the actual treatment, and the other is given a treatment exactly like the experimental treatment but without the active ingredient. Neither the placebo group nor the experimental group would know which treatment they are receiving, and in this way, these research participants are said to be blind controls. The term double blind indicates that the experimenters giving the medication also do not know which treatment is experimental and which is a placebo.

      In order to sort through the results of our experiments, we must be like detectives who constantly ask if there is another way to understand what was found. Our way of doing that is through research, logic, and doubt. We use research to design a study to consider alternative possibilities. We use logic to consider if our conclusions follow from the results. We use doubt to ask if there is a way to know if we are wrong.

      Concept Check

       What is the difference between the experimental group and the control group? Why is the control group important?

       What is an operational definition? How does it help advance scientific knowledge?

       How are the IV, the DV, and confounding variables related?

       What is a double-blind experiment, and what are we trying to control for by using that design?

      Designing an Experimental Study

      One goal of experimental research is to determine the relationship between the IV and the DV. Less bias in terms of demand characteristics related to both the participant and the experimenter aids in creating a logical relationship between the IV and DV.

      There are an additional four factors that are critical to sound inference (Figure 3.7). These are as follows:

      1 Participant selection

      2 Participant assignment

      3 Design of experiment

      4 Interpretation of relationship of IV to DV

      Participants in the Study

      It may seem simple to select subjects for an experiment. However, this is often a greater problem than it appears. The individuals selected for the study should be directly related to the hypothesis being tested. If you want to know if individuals with schizophrenia perform better on a memory test after drinking coffee, then of course you select individuals with schizophrenia. If you want to be able to apply the results to the 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

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