Supplementary Online Material
Social Laughter is Correlated With an Elevated Pain Threshold
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Dunbar, R., Baron, R., Frangou, A., Pearce, E., van Leeuwen, E.J.C., Stow, J.,
Partridge, P., MacDonald, I., Barra, V., & van Vugt, M.
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Methods
Participants were screened to exclude any who were pregnant, lactating or suffering
from a medical condition, or who had drunk alcohol or smoked within two hours prior
to the experiment. Diabetics were specifically excluded because of their lack of pain
sensitivity (McKinney et al., 1996). All designs were approved by local ethics boards,
and all subjects provided informed consent.
In Experiments 1 and 2, we used a frozen vacuum wine cooler sleeve placed over the
forearm as the assay for pain tolerance. Subjects were asked to say when they could
no longer stand the pain, and the duration noted (subject to a maximum of 180 sec to
avoid skin damage). These sleeves are open to the criticism that they might have been
less cold (and hence more bearable) in the second assay (after the video) than in the
first (before the video). To check for this, Experiment 3 used a more robust assay for
pain, namely a mercurial sphygmomanometer. Pilot trials suggested that the two
assays correlated, but that the sphygmomanometer produced less variable results than
the wine cooler sleeve. To induce ischemic pain, the cuff was inflated on participants’
non-dominant arm above the elbow at a steady rate (10mmHG/sec) by gentle
pumping to a maximum pressure of 260-280 mmHg. Subjects were again asked to say
when they could no longer stand the pain. The pressure at the point at which the
subject declared the pressure painful was noted to the nearest 5mmHg.
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Video material
Experiment 1
The comedy videos included excerpts from You’ve Been Framed, Mr Bean, and a
performance by the comedian Eddie Izzard; the control videos included Barking Mad
(a pet training documentary), excerpts from TV News and other factual TV
documentaries, and the religious programme Songs of Praise.
Experiment 2
The comedy videos included Father Ted, Friends and The Simpsons, while the control
videos included excerpts from a golfing programme, TV news and Eastenders (a
drama serial).
Experiment 3
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The comedy video was an excerpt from episode 95 of South Park; who watched a 31min video lecture on substance abuse (Substance Abuse: Current Topics: Episode 5,
“Understanding How Drugs Work”; Governors State University, June 2000).
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Experiment 4
The comedy video was from a performance DVD of the British comedian Michael
McIntyre; the neutral video was from a golfing instruction DVD.
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Experiment 5
The clips were either neutral (an excerpt from the BBC natural history series Walking
with Dinosaurs), affect positive (an excerpt showing lush, pleasant scenes and
animals from the Jungles episode of the BBC series Planet Earth) or funny (excerpts
from a performance by Dutch stand-up comedian Ronald Goedemondt and from
Funniest Home Videos).
Experiment 6
We made use of several Oxford-based troupes performing at the Fringe: the Oxford
Imps (an improvised stand-up comedy group) and the caste of two drama playlets
(Greek, a modern adaptation of the Oedipus story by Steven Birkhoff, and Same Time
Next Week, a modern drama about male friendships in the 21st Century, written by
Chris Leask and Martin West). The Comedy condition involved performers and
audience members at performances of the Oxford Imps. Performances comprised a set
of 7-8 improvised scenes and games performed by 7 performers (6 improvisers and
one Master of Ceremonies), in the style of the improvised comedy TV series “Who’s
Line Is It Anyway?” The comedy and drama shows were 50 and 75 mins long,
respectively. The show was performed in the same venue at the same time (3 pm)
every day to similar sized audiences. Each performer was in three or four scenes per
show and so all had roughly equal amounts of stage time. Audience members were
non-performing members of the troupe present at the same performances (technical
crew members or performing members not on stage that day who came to watch the
show). In the control (non-comedy) condition, the performers were the actors from the
playlets Greek and Same Time Next Week: each actor performed the experiment three
times. Audience participants at these two plays were recruited ad hoc from the Imps
crew.
Statistical analyses
The distribution of pain threshold differences was significantly different from
a normal distribution in only one of the 16 conditions in the 6 experiments: onesample Kolmogorov-Smirnov tests, 0.039p0.999; pooling the tests using Fisher’s
meta-analysis [Sokal & Rolf 1969, pp. 621-624] gave 2=24.76, df=32, p=0.857,
indicating that there was no underlying trend for the data to be significantly different
from a normal distribution). However, a similar analysis for rate of laughter yielded
two individual conditions that differed from normality (0.001p0.911), and an
overall pattern across the set of 12 conditions in which laughter occurred at all that
differed significantly from normality (Fisher’s meta-analysis: 2=47.17, df=24,
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p=0.003). An ln-transformation of [laughter rate +1] (to account for zero rates)
yielded an overall distribution that did not differ significantly from a normal
distribution (2=28.38, df=24, p=0.244). Parametric statistical tests were therefore
used on raw data for pain threshold and ln-transformed data for laughter rates. Since
there may be gender differences in pain threshold, we include gender as a factor in the
statistical analyses.
The underlying hypothesis we are testing is that laughter elevates pain
thresholds, and we need to show that the change in threshold from pre- to postintervention is significantly δ>0 after laughter, but not in the control condition when
there is no laughter. Since this is a directional hypothesis (we ask how likely it is that
the observed statistic is greater than 0 by chance alone), we use a one-sample, onetailed, directional t-test: when δ>0, p-values are one tailed as conventional, but when
δ<0 the likelihood that δ>0 is p=1-(0.5*pobs), where pobs is the conventional 2-tailed pvalue associated with the observed value of the test statistic.
Where appropriate, we use Fisher’s meta-analysis (Sokal & Rolf 1969, pp.
621-624) to test for consistent underlying trends in datasets from different
experiments. The test asks how likely it is to get a set of p-values as extreme as the
observed set by chance alone. Fisher showed that the absolute value of twice the sum
of the ln-transformed one-tailed directional p-values for individual experiments is
distributed as χ2 with df equal to twice the number of tests being combined
(irrespective of actual sample size). Thus, if three tests are combined, df=6.
References
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McKinney, C., Tims, F.C., Kumar, A.M., & Kumar, M. 1996. The effect of selected
classical music and spontaneous imagery on plasma β-endorphin. J. Behav. Med. 20,
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Sokal, R.R. & Rolf, F.J. 1969: Biometry. Freeman, San Francisco.
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Figure S1.
Median (50% and 95% ranges) laughter rates for control (neutral video: white bars)
and experimental (comedy video: dark grey bars) groups in Experiments 1, 2 and 4. In
Experiment 4, subjects watched a neutral video alone (white bar) and the comedy
video alone (light grey bar) or in a group (dark grey bar). Sample sizes are (left to
right): 18, 17, 16, 16, 22, 24, 12.
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