Further evidence for individual differences in placebo responding: an interactionist perspective.
ABSTRACT A prior investigation found that individuals low in optimism are more likely to follow a negative placebo (nocebo) expectation. The present study tested the hypothesis that individuals high in optimism are more likely to follow a positive placebo expectation.
Individuals (N=56) varying in their level of optimism were randomly assigned to one of three conditions. In the first condition, participants were given the expectation that a placebo sleep treatment would improve their sleep quality (placebo expectation condition). In the second condition, participants engaged in the same sleep treatment activity but were not given the positive placebo expectation (treatment control condition). Finally, a third group did not receive the positive placebo expectation and also did not engage in the placebo sleep treatment (no-placebo control condition).
Optimism was positively associated with better sleep quality in the placebo expectation condition (r=.48, P<.05). Optimism scores were not associated with better sleep quality in either the treatment control condition (r=-.17, P=.46) or the no-placebo control condition (r=-.24, P=.35).
Dispositional optimism relates to placebo responding. This relationship, however, is not manifested in a simple increase or decrease in all types of placebo responding. Rather, it appears that, as optimism increases, response to the positive placebo expectation increases, whereas response to nocebo expectation decreases. It is recommended that future research on personality and placebo effects consider the interaction between situational and dispositional variables.
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ABSTRACT: This article outlines and assesses the main theories of the placebo effect and suggests how they might sit together in a larger model of placebo etiology. Among the approaches considered are expectancy theory, emotional change theory, classical conditioning, and the biological approach. Although these are sometimes assumed to be competing models, in many cases they shed light on different pans of the placebo puzzle. Expectancies are the core of most placebo effects in human beings. The effects of expectancies are sometimes unmediated but in other cases are mediated by changes in emotional state, immune system function, perception, or behavior. Although expectancies are implicated in most placebo effects, a small number of placebo effects may be solely attributable to nonconscious contingency learning.Health Psychology 04/2004; 23(2):198-206. · 3.83 Impact Factor
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ABSTRACT: The renewed interest in placebo effects from psychological and methodological angles is manifested in two complementary facets: the causal relationship between placebo effects inside and outside of clinical trials and the continual effort to understand how the underlying mechanisms relate to notions of efficacy and effectiveness. The article challenges the premise that placebo effects can be measured precisely enough that variance attributed to "nonspecific" placebo effects can be hierarchically partitioned from variance attributed to other "more specific" elements of therapy and discusses some of the most important recent developments in the understanding of how placebos produce change through cognitive explanatory mechanisms, including efficacy, outcome, and response expectancies; reverse placebo effects; schemas; and biased-information processing. Although much is already known about the complexity of explanatory mechanisms in placebo and expectancy effects, there is still much to do before establishing causal relationships and developing valid treatments based on this knowledge.Evaluation & the Health Professions 01/2003; 25(4):436-64. · 1.48 Impact Factor