| The placebo effect, a positive outcome resulting from the belief
that a beneficial treatment has been received, is widely acknowledged but
little understood. It has been suggested that placebo responsiveness, the
degree to which an individual will respond to a placebo, might vary in the
population. The study aimed to identify placebo-responsive participants
from a previously published paper that examined the effects of caffeine
and placebos on cycling performance. A quantitative model of placebo responsiveness
was defined. 14 male participants were subsequently classified as either
placebo responsive or non-responsive. Interviews were conducted to corroborate
these classifications. Secondary quantitative analyses of performance data
were conducted to identify further placebo responses. Finally, the five
factor model of personality was used to explore relationships between personality
and placebo responsiveness. Overall, 5 of 14 participants were classified
as placebo responsive. Performance data suggested that 2 participants were
placebo responsive whilst 12 were not. Interview data corroborated experimental
data for these participants and for 9 of the remainder, however it suggested
that the remaining 3 had experienced placebo effects. Secondary quantitative
analysis revealed that performance for these 3 participants, whilst no better
than for non-responsive participants, was associated with substantially
increased oxygen uptake in the 2 conditions in which participants believed
caffeine had been administered (7.0% ± 15.1; 95% confidence intervals -2.6
to 16.7, and 6.0% ± 15.4; -3.9 to 15.9 respectively). Finally, data suggested
that the personality factors of extroversion, agreeableness, openness and
neuroticism may relate to placebo responding. Placebo effects such as pain
tolerance and fatigue resistance might be experienced by a percentage of
participants but might not always be manifest in objective measures of performance.
Key words: Caffeine; personality; placebo effect; nocebo effect;
qualitative.
|
,
Abigail J. Foad and Damian A. Coleman