Presenting a sham treatment as personalised increases the placebo effect in a randomised controlled trial
- Integrated Program in Neuroscience, McGill University, Canada
- Department of Psychology, Harvard University, United States
- Department of Psychology, McGill University, Canada
Figures
Figure 1
Participants completed sham medical tests and then rated pain stimulations in a room with various medical equipment.
Figure 2
On half of the stimulations, participants used a complex placebo machine with dials, vibration, and flashing lights to help reduce pain.
This machine was presented as either personalised to their test results or as generally effective. The machine’s design (over a dozen of switches and dials) allowed us to simulate complex personalisation to the participants’ profile.
Figure 3
Procedure for the confirmatory study.
We first asked participants to complete personality questionnaires and calibrated heat stimulations to their individual pain perception. Participants then completed sham medical tests (i.e., genetics, skin conductance) before being randomised to receive the placebo machine described as personalised to their sham test results or not (control). A research assistant blind to the experimental condition then led participants through a pain rating task that was similar to the calibration. On half of the heat stimulations, participants used the machine (turned on) to counteract the heat pain (on the other half, the machine was turned off). In the conditioning phase, we simulated machine effectiveness by covertly reducing the intensity of pain stimulations when the machine was turned on. For the testing phase, we kept the temperature stable and quantified the placebo effect as the difference between the trials with the machine off and on.
Figure 4
Participants in the personalised group reported nearly twice the reduction in pain intensity (A) and unpleasantness (B; N=17).
The placebo effect was calculated as ratings with the machine off – machine on. Black dots show means, coloured dots show individual raw scores, violin widths show frequency, and error bars show 95% confidence intervals.
Figure 5
Individual pain score changes with the placebo machine turned on or off for pain intensity (A) and unpleasantness (B).
Large coloured dots show means, small coloured dots show individual scores, and error bars show 95% confidence intervals.
Figure 6
Participants in the personalised group reported higher placebo effects than those in the control group for pain intensity (A) and unpleasantness (B; N=85).
The panels show changes calculated as ratings with the machine off – machine on. Black dots show means, coloured dots show individual raw scores, violin widths show frequency, and error bars show 95% confidence intervals.
Figure 7
Individual pain score changes with the placebo machine turned on or off for pain intensity (A) and unpleasantness (B).
Large coloured dots show means, small coloured dots show individual scores, and error bars show 95% confidence intervals.
Figure 8
Exploratory predictors of placebo effects on pain intensity (N=85).
Participants high in Need for uniqueness (A), Attention regulation (B), Emotion awareness (C), and Noticing (D) showed stronger placebo effects with a sham-personalised machine than those in the control group. Shaded regions denote 95% confidence intervals and correlations are between the trait and the pain ratings in each group.
Figure 9
Expectations as a predictor of placebo effects with groups combined (N=84).
Dots show individual scores and shaded regions denote 95% confidence intervals.
Appendix 1—figure 1
The differences in pain intensity and unpleasantness during the conditioning phase of the confirmatory study.
Dots show means and error bars show 95% confidence intervals.
Appendix 1—figure 2
Personality traits that significantly moderated the placebo effects of personalisation (N=85).
Shaded regions show 95% confidence intervals, equations represent proportion of variance explained by each group.
Appendix 1—figure 3
Correlations between all personality traits measured as potential predictors of placebo effects of personalisation.
Tables
Appendix 1—table 1
Regression results of all personality predictors of increased placebo effects on pain intensity.
We only tested interactions to reduce the probability of Type I errors; all tests were exploratory. Significant interactions (change in pain ratings × personality trait; two-tailed p <.05) are bolded.
| Personality trait | Predictor | Standardised β | SE | df | t | p |
|---|---|---|---|---|---|---|
| Attention regulation | (Intercept) | 0.034 | 0.411 | 591 | 0.084 | .933 |
| Condition | –0.032 | 0.549 | 81 | –0.059 | .953 | |
| Machine | –0.167 | 0.175 | 591 | –0.950 | .342 | |
| Attention regulation | 0.020 | 0.143 | 81 | 0.138 | .891 | |
| Interaction | –0.177 | 0.083 | 591 | –2.142 | .033 | |
| Noticing | (Intercept) | –0.158 | 0.46 | 591 | –0.343 | .732 |
| Condition | 0.058 | 0.623 | 81 | 0.093 | .926 | |
| Machine | –0.414 | 0.198 | 591 | –2.094 | .037 | |
| Noticing | 0.077 | 0.139 | 81 | 0.554 | .581 | |
| Interaction | –0.167 | 0.081 | 591 | –2.065 | .039 | |
| Not-worrying | (Intercept) | 0.271 | 0.365 | 591 | 0.743 | .458 |
| Condition | –0.121 | 0.493 | 81 | –0.244 | .807 | |
| Machine | 0.047 | 0.157 | 591 | 0.297 | .766 | |
| Not-worrying | –0.074 | 0.138 | 81 | –0.537 | .593 | |
| Interaction | 0.080 | 0.082 | 591 | 0.981 | .327 | |
| Self-regulation | (Intercept) | –0.267 | 0.401 | 591 | –0.666 | .506 |
| Condition | 0.272 | 0.541 | 81 | 0.502 | .617 | |
| Machine | –0.095 | 0.173 | 591 | –0.547 | .584 | |
| Self-regulation | 0.132 | 0.140 | 81 | 0.940 | .350 | |
| Interaction | –0.077 | 0.082 | 591 | –0.943 | .346 | |
| Emotion awareness | (Intercept) | –0.333 | 0.413 | 591 | –0.806 | .421 |
| Condition | 0.693 | 0.591 | 81 | 1.172 | .244 | |
| Machine | –0.435 | 0.179 | 591 | –2.426 | .016 | |
| Emotion awareness | 0.130 | 0.121 | 81 | 1.078 | .284 | |
| Interaction | –0.203 | 0.077 | 591 | –2.643 | .008 | |
| Not-distracting | (Intercept) | 0.739 | 0.335 | 591 | 2.207 | .028 |
| Condition | –1.030 | 0.522 | 81 | –1.974 | .052 | |
| Machine | –0.205 | 0.147 | 591 | –1.391 | .165 | |
| Not-distracting | –0.312 | 0.147 | 81 | –2.119 | .037 | |
| Interaction | –0.134 | 0.100 | 591 | –1.350 | .177 | |
| Trusting | (Intercept) | 0.299 | 0.423 | 591 | 0.707 | .480 |
| Condition | –0.945 | 0.572 | 81 | –1.651 | .103 | |
| Machine | 0.013 | 0.185 | 591 | 0.069 | .945 | |
| Trusting | –0.065 | 0.123 | 81 | –0.529 | .598 | |
| Interaction | –0.037 | 0.073 | 591 | –0.503 | .615 | |
| Body listening | (Intercept) | –0.296 | 0.327 | 591 | –0.904 | .366 |
| Condition | 0.155 | 0.447 | 81 | 0.348 | .729 | |
| Machine | –0.106 | 0.142 | 591 | –0.749 | .454 | |
| Body listening | 0.157 | 0.123 | 81 | 1.276 | .206 | |
| Interaction | –0.068 | 0.071 | 591 | –0.947 | .344 | |
| Openness to experience | (Intercept) | 0.387 | 0.839 | 591 | 0.462 | .644 |
| Condition | 0.515 | 1.205 | 81 | 0.427 | .671 | |
| Machine | –0.129 | 0.362 | 591 | –0.356 | .722 | |
| Openness to experience | –0.008 | 0.023 | 81 | –0.360 | .720 | |
| Interaction | –0.003 | 0.014 | 591 | –0.226 | .821 | |
| Conscientiousness | (Intercept) | 0.062 | 0.646 | 591 | 0.097 | .923 |
| Condition | –0.251 | 0.877 | 81 | –0.286 | .776 | |
| Machine | 0.371 | 0.277 | 591 | 1.336 | .182 | |
| Conscientiousness | 0.001 | 0.020 | 81 | 0.043 | .966 | |
| Interaction | 0.027 | 0.012 | 591 | 2.281 | .023 | |
| Extraversion | (Intercept) | 0.625 | 0.544 | 591 | 1.148 | .251 |
| Condition | –0.246 | 0.825 | 81 | –0.298 | .766 | |
| Machine | –0.499 | 0.233 | 591 | –2.136 | .033 | |
| Extraversion | –0.021 | 0.021 | 81 | –1.015 | .313 | |
| Interaction | –0.013 | 0.013 | 591 | –0.953 | .341 | |
| Agreeableness | (Intercept) | 0.451 | 0.738 | 591 | 0.611 | .541 |
| Condition | –0.763 | 1.416 | 81 | –0.538 | .592 | |
| Machine | 0.323 | 0.317 | 591 | 1.017 | .310 | |
| Agreeableness | –0.011 | 0.022 | 81 | –0.500 | .618 | |
| Interaction | 0.001 | 0.018 | 591 | 0.061 | .951 | |
| Neuroticism | (Intercept) | 0.578 | 0.547 | 591 | 1.057 | .291 |
| Condition | 0.093 | 0.803 | 81 | 0.115 | .908 | |
| Machine | –0.371 | 0.236 | 591 | –1.573 | .116 | |
| Neuroticism | –0.020 | 0.021 | 81 | –0.920 | .361 | |
| Interaction | –0.008 | 0.013 | 591 | –0.594 | .553 | |
| Fear of pain | (Intercept) | 0.296 | 0.735 | 591 | 0.403 | .687 |
| Condition | –1.179 | 1.070 | 81 | –1.102 | .274 | |
| Machine | –0.493 | 0.318 | 591 | –1.553 | .121 | |
| Fear of pain | –0.002 | 0.009 | 81 | –0.283 | .778 | |
| Interaction | –0.007 | 0.005 | 591 | –1.211 | .226 | |
| Pain catastrophising | (Intercept) | –0.221 | 0.282 | 591 | –0.786 | .432 |
| Condition | 0.268 | 0.449 | 81 | 0.596 | .553 | |
| Machine | –0.095 | 0.122 | 591 | –0.776 | .438 | |
| Pain catastrophising | 0.014 | 0.012 | 81 | 1.246 | .216 | |
| Interaction | –0.009 | 0.008 | 591 | –1.104 | .270 |
Appendix 1—table 2
Regression results of all personality predictors of increased placebo effects on pain unpleasantness.
Significant interactions (change in pain ratings × personality trait; two-tailed p <.05) are bolded.
| Personality trait | Predictor | β | SE | df | t | p |
|---|---|---|---|---|---|---|
| Attention regulation | (Intercept) | 0.036 | 0.413 | 591 | 0.086 | .931 |
| Condition | 0.052 | 0.552 | 81 | 0.094 | .925 | |
| Machine | –0.302 | 0.176 | 591 | –1.710 | .088 | |
| Attention regulation | –0.010 | 0.144 | 81 | –0.067 | .947 | |
| Interaction | –0.279 | 0.083 | 591 | –3.349 | .001 | |
| Noticing | (Intercept) | –0.416 | 0.460 | 591 | –0.905 | .366 |
| Condition | 0.445 | 0.623 | 81 | 0.714 | .477 | |
| Machine | –0.545 | 0.200 | 591 | –2.724 | .007 | |
| Noticing | 0.134 | 0.139 | 81 | 0.967 | .336 | |
| Interaction | –0.212 | 0.082 | 591 | –2.590 | .010 | |
| Not-worrying | (Intercept) | 0.357 | 0.362 | 591 | 0.988 | .324 |
| Condition | 0.309 | 0.488 | 81 | 0.632 | .529 | |
| Machine | 0.008 | 0.159 | 591 | 0.052 | .958 | |
| Not-worrying | –0.144 | 0.137 | 81 | –1.049 | .297 | |
| Interaction | 0.078 | 0.083 | 591 | 0.944 | .346 | |
| Self-regulation | (Intercept) | –0.343 | 0.403 | 591 | –0.851 | .395 |
| Condition | 0.443 | 0.544 | 81 | 0.814 | .418 | |
| Machine | –0.215 | 0.175 | 591 | –1.227 | .220 | |
| Self-regulation | 0.132 | 0.141 | 81 | 0.932 | .354 | |
| Interaction | –0.133 | 0.083 | 591 | –1.613 | .107 | |
| Emotion awareness | (Intercept) | –0.463 | 0.417 | 591 | –1.111 | .267 |
| Condition | 0.679 | 0.596 | 81 | 1.139 | .258 | |
| Machine | –0.440 | 0.182 | 591 | –2.419 | .016 | |
| Emotion awareness | 0.146 | 0.122 | 81 | 1.198 | .234 | |
| Interaction | –0.206 | 0.078 | 591 | –2.644 | .008 | |
| Not-distracting | (Intercept) | 0.632 | 0.338 | 591 | 1.869 | .062 |
| Condition | –0.961 | 0.527 | 81 | –1.824 | .072 | |
| Machine | –0.207 | 0.149 | 591 | –1.389 | .165 | |
| Not-distracting | –0.296 | 0.149 | 81 | –1.992 | .050 | |
| Interaction | –0.184 | 0.101 | 591 | –1.823 | .069 | |
| Trusting | (Intercept) | 0.206 | 0.430 | 591 | 0.479 | .632 |
| Condition | –0.580 | 0.582 | 81 | –0.997 | .322 | |
| Machine | –0.065 | 0.188 | 591 | –0.346 | .730 | |
| Trusting | –0.061 | 0.125 | 81 | –0.485 | .629 | |
| Interaction | –0.008 | 0.074 | 591 | –0.108 | .914 | |
| Body listening | (Intercept) | –0.427 | 0.325 | 591 | –1.315 | .189 |
| Condition | 0.141 | 0.444 | 81 | 0.317 | .752 | |
| Machine | –0.213 | 0.143 | 591 | –1.484 | .138 | |
| Body listening | 0.180 | 0.122 | 81 | 1.471 | .145 | |
| Interaction | –0.168 | 0.072 | 591 | –2.331 | .020 | |
| Openness to experience | (Intercept) | 0.374 | 0.845 | 591 | 0.442 | .658 |
| Condition | 0.055 | 1.214 | 81 | 0.045 | .964 | |
| Machine | –0.287 | 0.363 | 591 | –0.790 | .430 | |
| Openness to experience | –0.010 | 0.023 | 81 | –0.433 | .666 | |
| Interaction | –0.037 | 0.014 | 591 | –2.655 | .008 | |
| Conscientiousness | (Intercept) | –0.042 | 0.654 | 591 | –0.064 | .949 |
| Condition | 0.409 | 0.888 | 81 | 0.460 | .647 | |
| Machine | 0.136 | 0.282 | 591 | 0.482 | .630 | |
| Conscientiousness | 0.002 | 0.021 | 81 | 0.081 | .936 | |
| Interaction | 0.020 | 0.012 | 591 | 1.608 | .108 | |
| Extraversion | (Intercept) | 0.541 | 0.548 | 591 | 0.987 | .324 |
| Condition | –0.531 | 0.831 | 81 | –0.639 | .525 | |
| Machine | –0.380 | 0.237 | 591 | –1.603 | .110 | |
| Extraversion | –0.021 | 0.021 | 81 | –1.004 | .318 | |
| Interaction | –0.018 | 0.014 | 591 | –1.326 | .185 | |
| Agreeableness | (Intercept) | 0.364 | 0.743 | 591 | 0.489 | .625 |
| Condition | –0.723 | 1.427 | 81 | –0.507 | .614 | |
| Machine | 0.250 | 0.322 | 591 | 0.777 | .438 | |
| Agreeableness | –0.011 | 0.022 | 81 | –0.484 | .629 | |
| Interaction | 0.007 | 0.018 | 591 | 0.371 | .710 | |
| Neuroticism | (Intercept) | 0.029 | 0.554 | 591 | 0.053 | .958 |
| Condition | –0.016 | 0.814 | 81 | –0.020 | .984 | |
| Machine | –0.338 | 0.239 | 591 | –1.414 | .158 | |
| Neuroticism | –0.001 | 0.022 | 81 | –0.037 | .970 | |
| Interaction | –0.015 | 0.014 | 591 | –1.137 | .256 | |
| Fear of pain | (Intercept) | –0.156 | 0.742 | 591 | –0.210 | .834 |
| Condition | –0.405 | 1.080 | 81 | –0.375 | .709 | |
| Machine | –0.441 | 0.322 | 591 | –1.370 | .171 | |
| Fear of pain | 0.002 | 0.009 | 81 | 0.231 | .818 | |
| Interaction | –0.004 | 0.006 | 591 | –0.671 | .502 | |
| Pain catastrophising | (Intercept) | –0.404 | 0.278 | 591 | –1.452 | .147 |
| Condition | 0.064 | 0.444 | 81 | 0.143 | .886 | |
| Machine | –0.098 | 0.124 | 591 | –0.796 | .426 | |
| Pain catastrophising | 0.019 | 0.011 | 81 | 1.678 | .097 | |
| Interaction | –0.010 | 0.008 | 591 | –1.172 | .242 |
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Presenting a sham treatment as personalised increases the placebo effect in a randomised controlled trial
eLife 12:e84691.
https://doi.org/10.7554/eLife.84691
