Ebook Methods in behavioral research (11th edition): Part 2

www.downloadslide.com 9 Conducting Experiments LEARNING OBJECTIVES Distinguish between straightforward and staged manipulations of an independent variable. Describe the three types of dependent variables: self-report, behavioral, and physiological. Discuss sensitivity of a dependent variable, contrasting floor effects and ceiling effects. Describe ways to control participant expectations and experimenter expectations. List the reasons for conducting pilot studies. Describe the advantages of including a manipulation check in an experiment. 173 www.downloadslide.com he previous chapters have laid the foundation for planning a research in-vestigation. In this chapter, we will focus on some very practical aspects of conducting research. How do you select the research participants? What should you consider when deciding how to manipulate an independent variable? What should you worry about when you measure a variable? What do you do when the study is completed? SELECTING RESEARCH PARTICIPANTS The focus of your study may be children, college students, elderly adults, employees, rats, pigeons, or even cockroaches or flatworms; in all cases, the participants or subjects must somehow be selected. The method used to select participants can have a profound impact on external validity. Remember that external validity is defined as the extent to which results from a study can be generalized to other populations and settings. Recall from Chapter 7 that most research projects involve sampling re-search participants from a population of interest. The population is composed of all of the individuals of interest to the researcher. Samples may be drawn from the population using probability sampling or nonprobability sampling techniques. When it is important to accurately describe the population, you must use probability sampling. This is why probability sampling is so crucial when conducting scientific polls. Much research, on the other hand, is more interested in testing hypotheses about behavior: attempting to detect whether X causes Y rather than describing a population. Here, the two focuses of the study are the relationships between the variables being studied and tests of pre-dictions derived from theories of behavior. In such cases, the participants may be found in the easiest way possible using nonprobability sampling methods, also known as haphazard or “convenience” methods. You may ask students in introductory psychology classes to participate, knock on doors in your dorm to find people to be tested, or choose a class in which to test children simply because you know the teacher. Nothing is wrong with such methods as long as you recognize that they affect the ability to generalize your results to some larger population. In Chapter 14, we examine the issues of generalizing from the rather atypical samples of college students and other conveniently obtained research participants. You will also need to determine your sample size. How many participants will you need in your study? In general, increasing your sample size increases the likelihood that your results will be statistically significant, because larger samples provide more accurate estimates of population values (see Table 7.2). Most researchers take note of the sample sizes in the research area being studied and select a sample size that is typical for studies in the area. A more formal approach to selecting a sample size, called power analysis, is discussed in Chapter 13. 174 www.downloadslide.com Manipulating the Independent Variable 175 MANIPULATING THE INDEPENDENT VARIABLE To manipulate an independent variable, you have to construct an operational definition of the variable (see Chapter 4). That is, you must turn a conceptual variable into a set of operations—specific instructions, events, and stimuli to be presented to the research participants. The manipulation of the independent variable, then, is when a researcher changes the conditions to which participants are exposed. In addition, the independent and dependent variables must be in-troduced within the context of the total experimental setting. This has been called setting the stage (Aronson, Brewer, & Carlsmith, 1985). Setting the Stage In setting the stage, you usually have to supply the participants with the infor-mation necessary for them to provide their informed consent to participate (in-formed consent is covered in Chapter 3). This generally includes information about the underlying rationale of the study. Sometimes, the rationale given is completely truthful, although only rarely will you want to tell participants the actual hypothesis. For example, you might say that you are conducting an ex-periment on memory when, in fact, you are studying a specific aspect of memory (your independent variable). If participants know what you are studying, they may try to confirm the hypothesis, or they may try to look good by behaving in the most socially acceptable way. If you find that deception is necessary, you have a special obligation to address the deception when you debrief the participants at the conclusion of the experiment. There are no clear-cut rules for setting the stage, except that the experimen-tal setting must seem plausible to the participants, nor are there any clear-cut rules for translating conceptual variables into specific operations. Exactly how the variable is manipulated depends on the variable and the cost, practicality, and ethics of the procedures being considered. Types of Manipulations Straightforward manipulations Researchers are usually able to manipulate an independent variable with relative simplicity by presenting written, verbal, or visual material to the participants. Such straightforward manipulations manipulate variables with instructions and stimulus presenta-tions. Stimuli may be presented verbally, in written form, via videotape, or with a computer. Let’s look at a few examples. Goldstein, Cialdini, and Griskevicius (2008) were interested in the influ-ence of signs that hotels leave in their bathrooms encouraging guests to reuse their towels. In their research, they simply printed signs that were hooked on towel shelves in the rooms of single guests staying at least two nights. In a standard message, the sign read “HELP SAVE THE ENVIRONMENT. You can show your respect of nature and help save the environment by reusing towels during your stay.” In this case, 35% of the guests reused their towels on www.downloadslide.com 176 Chapter 9 � Conducting Experiments the second day. Another condition invoked a social norm that other people are reusing towels: “JOIN YOUR FELLOW GUESTS IN HELPING TO SAVE THE ENVIRONMENT. Almost 75% of guests who are asked to participate in our new resource savings program do help by using their towels more than once. You can join your fellow guests in this program to save the environ-ment by reusing your towels during your stay.” This sign resulted in 44% reusing their towels. As you might expect, the researchers have extended this research to study ways that the sign can be even more effective in increasing conservation. Studies on jury decisions often ask participants to read a description of a jury trial in which a crucial piece of information is varied. Bornstein (1998) studied the effect of the severity of injury on product liability judgments. In the low-severity condition, participants read about a case in which a woman taking birth control pills had been diagnosed with cancer. In a low-severity condition, the cancer was detected early, one ovary was removed, the woman could still have children, and future prognosis was good. In the high-severity condition, the cancer was detected late, both ovaries were removed so pregnancy would not be possible, and the future prognosis was poor. The evidence on whether the pills could be responsible for the cancer was the same in both conditions, thus product liability judgments should be the same in both conditions. Neverthe-less, the severity information affected liability judgments: The pill manufacturer was found liable by 40% of the participants in the high-severity condition versus 21% in the low-severity condition. Most memory research relies on straightforward manipulations. For exam-ple, Coltheart and Langdon (1998) displayed lists of words to participants and later measured recall. The word lists differed on phonological similarity: Some lists had words that sounded similar, such as cat, map, and pat, and other lists had dissimilar words such as mop, pen, and cow. They found that lists with dis-similar words are recalled more accurately. In a more complex memory study, Reeve and Aggleton (1998) presented a script of a future episode of a British soap opera called The Archers to both fans (“experts”) and people unfamiliar with the show. In one condition, the script was typical of an actual episode of the program—the Archers visit a livestock market. In the other condition, the script was atypical—the Archers visit a boat show. The characters and basic structure of the show were identical in the two conditions. After reading the script, the participants were given a measure of retention of the details of the episode. They found that being an expert aided retention only when the story was a typical one. In the atypical condition, both fans and nonfans had equal retention. Reeve and Aggleton concluded that the benefits of being an expert are limited. As a final example of a straightforward manipulation, consider a study by Mazer, Murphy, and Simonds (2009) on the effect of college teacher self-disclosure (via Facebook) on perceptions of teacher effectiveness. For this study, students read one of three Facebook profiles that were created for a volunteer teacher, one for each of the high-, medium-, and low-disclosure www.downloadslide.com Manipulating the Independent Variable 177 conditions. Level of disclosure was manipulated by changing the number and nature of photographs, biographical information, favorite movies/ books/quotes, campus groups, and posts on “the wall.” After viewing the profile to which they were assigned, participants rated the teacher on sev-eral dimensions. Higher disclosure resulted in perceptions of greater caring and trustworthiness; however, disclosure was not related to perceptions of teacher competence. You will find that most manipulations of independent variables in all areas of research are straightforward. Researchers vary the difficulty of mate-rial to be learned, motivation levels, the way questions are asked, characteris-tics of people to be judged, and a variety of other factors in a straightforward manner. Staged manipulations Other manipulations are less straightforward. Sometimes, it is necessary to stage events during the experiment in order to ma-nipulate the independent variable successfully. When this occurs, the manipula-tion is called a staged manipulation or event manipulation. Staged manipulations are most frequently used for two reasons. First, the researcher may be trying to create some psychological state in the participants, such as frustration, anger, or a temporary lowering of self-esteem. For example, Zitek and her colleagues studied what is termed a sense of entitlement (Zitek, Jordan, Monin, & Leach, 2010). Their hypothesis is that the feeling of being un-fairly wronged leads to a sense of entitlement and, as a result, the tendency to be more selfish with others. In their study, all participants played a computer game. The researchers programmed the game so that some participants would lose when the game crashed. This is an unfair outcome, because the partici-pants lost for no good reason. Participants in the other condition also lost, but they thought it was because the game itself was very difficult. The participants experiencing the broken game did in fact behave more selfishly after the game; they later allocated themselves more money than deserved when competing with another participant. Second, a staged manipulation may be necessary to simulate some situa-tion that occurs in the real world. Recall the Milgram obedience experiment that was described in Chapter 3. In that study, an elaborate procedure—ostensibly to study learning—was constructed to actually study obedience to an authority. Or consider a study on computer multitasking conducted by Bowman, Levine, Waite, and Gendron (2009), wherein students read academic material presented on a computer screen. In one condition, the participants received and responded to instant messages while they were reading. Other participants did not receive any messages. Student performance on a test was equal in the two conditions. However, students in the instant message condition took longer to read the material (after the time spent on the message was subtracted from the total time working on the computer). Staged manipulations frequently employ a confederate (sometimes termed an “accomplice”). Usually, the confederate appears to be another participant ... - tailieumienphi.vn