CMAJ • December 4, 2007 • 177(12)
© 2007 Canadian Medical Association or its licensors
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about the potential for bias during randomization of partici-
pants in clinical trials.1–5I designed the Chocolate Happiness
Undergoing More Pleasantness (CHUMP) study to compare the
effects of dark chocolate, milk chocolate and “normal” choco-
late consumption on happiness. The CHUMP study was a
double-blinded clinical trial, and it demonstrated the difficul-
ties associated with performing a truly blinded clinical trial.
he randomized controlled trial is the “gold standard” for
testing the beneficial and harmful effects of interven-
tions. There has been a growing concern in the literature
The CHUMP study was conducted over a 1-month period at a
tertiary pediatric health care centre. Between Oct. 15, 2006,
and Nov. 15, 2006, 144 adults were asked to participate in the
CHUMP study. Owing to the study’s popularity and the in-
sistence of the research ethics board, an additional 36 adults
were added to the study, for a total of 180 participants (108
women, 72 men).The research ethics board of the Chocolate
Consumption Society approved the CHUMP study.
The participants were randomized into 3 study groups.
Group 1 received 1 dark chocolate bar (50 g, > 90% cocoa)
each day, and group 2 received 1 milk chocolate bar (50 g,
20% cocoa) each day. Members of group 3 did not receive any
additional chocolate; however, they continued with their nor-
mal chocolate-eating habits.
Each participant rated their happiness before and after the
study using a visual analog scale (0 = unhappy, 10 = happy).
Participants were also asked to rate their health, global happi-
ness and personal work history (0 = worst, 10 = best). In or-
der to establish participants’ baseline chocolate-eating
habits, participants were asked the frequency of chocolate
consumption and the amount consumed on a daily basis to
give a total chocolate bar day-equivalent. The total chocolate
bar day-equivalent included both dark chocolate bar day-
equivalents and milk chocolate bar day-equivalents.
I anaylzed contingency tables with χ2tests, and I used analy-
sis of variance to test for differences in the mean chocolate con-
sumption among the 3 groups. No specific research funding
was obtained for the CHUMP study; however, Costco provided a
generous discount toward the purchase of the boxes of choco-
late consumed in the study.
The CHUMP study began with 60 participants in each group.
Despite my efforts to keep the study groups blinded, some of
the participants changed groups mid-study. Indeed, those in the
control group (who received no extra chocolate) decided to start
A clinical trial gone awry: the Chocolate Happiness
Undergoing More Pleasantness (CHUMP) study
Research of a holiday kind
The randomized controlled trial is the “gold standard” for
evaluating the benefits and harms of interventions. The
Chocolate Happiness Undergoing More Pleasantness
(CHUMP) study was designed to compare the effects of dark
chocolate, milk chocolate and normal chocolate consumption
on happiness. Although the intention-to-treat analysis showed
that participants who received either dark or milk chocolate
were happier than those who received no additional choco-
late, the actual-consumption analysis showed that there were
no differences between any of the groups. The reason for this
result is that many participants switched groups mid-study be-
cause of their personal chocolate preferences. Although the
CHUMP study was pleasurable, it demonstrated the diffi-
culties associated with performing a truly blinded clinical trial.