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CHAPTER 9: Single-Case Designs and Small-n Research 289unambiguously the specific factors that produce a particular event. One disadvantageof the case study method is that cause-effect conclusions can rarely bedrawn on the basis of results that are obtained from case studies. This disadvantagearises primarily because researchers are unable to control extraneous variablesin case studies. Thus, the behavior changes that take place in case studiescan be explained by several plausible alternative hypotheses.Consider, for instance, the treatment of Susan through SMT reported byKirsch (1978). Although Susan apparently benefited from the SMT therapy, canwe be sure that SMT caused her improvement? Many illnesses and emotionaldisorders improve without treatment. Case study researchers must always considerthe alternative hypothesis that individuals may have improved withouttreatment. In addition, several aspects of the situation may have been responsiblefor Susan’s improvement. Her care was in the hands of a “clinical psychologist”who provided reassurance. Also, Susan may have changed her attitudestoward herself because of the insights of her therapist and the feedback shereceived from her test results, not because of SMT. The therapist also askedSusan, as part of her therapy, to rehearse anxiety-arousing situations covertlyand overtly. This technique is similar to rehearsal desensitization, which mayitself be an effective treatment (Rimm & Masters, 1979).Because several treatments were used simultaneously, we cannot argueconvincingly that SMT was the unambiguous “cause” of Susan’s improvement.As we have seen, Kirsch himself was sensitive to the limitations of the casestudy method and suggested that the inferences he drew based on the resultsof his study should be considered tentative until they were investigated morerigorously.The difficulty of drawing cause-and-effect conclusions from case studies isalso illustrated by results of recent research on amusia. As we noted previously,theories attempting to link music appreciation and language developmentappear to be weakened when individuals are discovered who have normalspeech perception and speech production, but lack the ability to “hear” music.Nevertheless, there is evidence for many forms of amusia, each, most likely,with its own neural basis. Some cases involve the perception of rhythm; othersthe recognition of melodies; and still others an inability to recognize discordantsounds (see Sacks, 2007). Thus, more research is needed to give us a better understandingof the relationship between music and language abilities.Potential Sources of Bias The outcome of a case study often depends on conclusionsdrawn by a researcher who is both participant and observer (Bolgar,1965). That is, a therapist observes the client’s behavior and participates in thetherapeutic process. It is reasonable to assume that the therapist may be motivatedto believe that the treatment helps the client. As a result, the therapist,even if well intentioned, may not accurately observe the client’s behavior. Thepotential for biased interpretation is not peculiar to the case study method. Wehave previously considered the problems of observer bias (Chapter 4) and experimenterbias (Chapter 6).The outcome of a case may be based mainly on the “impressions” of the observer(Hersen & Barlow, 1976). For example, Kirsch (1978) described the client