Appendix 1—table 2. Results of multiple linear regression analyses with expectations, prior experience and psychological factors as independent variables and placebo effect or nocebo effect as the dependent variable.
| Beta | Std error | t-value | P-value | |
|---|---|---|---|---|
| Day 1: placebo effect | ||||
| Intercept | 1.294 | 22.168 | ||
| Expected improvement pre-conditioning (GEEE) | –0.531 | 0.750 | –0.708 | 0.481 |
| Conditioning placebo effect (VAS rating) | 0.303 | 0.097 | 3.120 | 0.002** |
| Expected improvement on day 1 (GEEE) | 0.626 | 0.575 | 1.088 | 0.280 |
| Psychological variables: | ||||
| Somatosensory amplification | –0.654 | 0.227 | –2.877 | 0.005** |
| Trait anxiety | 0.042 | 0.334 | 0.126 | 0.900 |
| Trait depression | 0.220 | 0.308 | 0.712 | 0.478 |
| Behavioural inhibition | –1.528 | 3.100 | –0.493 | 0.623 |
| Behavioural activation | 4.922 | 3.299 | 1.492 | 0.139 |
| Pain catastrophising | 0.070 | 0.136 | 0.511 | 0.611 |
| Experimenter warmth | –4.161 | 3.027 | –1.375 | 0.173 |
| Experimenter competence | 4.732 | 3.742 | 1.265 | 0.209 |
| Day 1: nocebo effect | ||||
| Intercept | –36.384 | 15.752 | –2.310 | 0.023 |
| Expected worsening pre-conditioning (GEEE) | 0.402 | 0.470 | 0.856 | 0.394 |
| Conditioning nocebo effect (VAS rating) | 0.131 | 0.078 | 1.690 | 0.095 |
| Expected worsening on day 1 (GEEE) | 0.200 | 0.442 | 0.454 | 0.651 |
| Psychological variables: | ||||
| Somatosensory amplification | –0.206 | 0.167 | –1.235 | 0.220 |
| Trait anxiety | 0.445 | 0.255 | 1.745 | 0.084 |
| Trait depression | –0.096 | 0.225 | –0.425 | 0.672 |
| Behavioural inhibition | 4.011 | 2.312 | 1.735 | 0.086 |
| Behavioural activation | 4.800 | 2.416 | 1.987 | 0.050 |
| Pain catastrophising | 0.084 | 0.098 | 0.857 | 0.394 |
| Experimenter warmth | –0.352 | 2.314 | –0.152 | 0.879 |
| Experimenter competence | 5.791 | 2.801 | 2.067 | 0.042* |
| Day 8: placebo effect | ||||
| Intercept | 17.843 | 14.498 | 1.231 | 0.222 |
| Expected improvement pre-conditioning (GEEE) | –0.702 | 0.496 | –1.417 | 0.160 |
| Conditioning placebo effect (VAS rating) | 0.063 | 0.073 | 0.863 | 0.391 |
| Expected improvement on day 1 (GEEE) | –0.949 | 0.507 | –1.872 | 0.065 |
| Placebo effect on day 1 (VAS rating) | 0.382 | 0.071 | 5.343 | <0.001*** |
| Expected improvement on day 8 (GEEE) | 1.131 | 0.536 | 2.110 | 0.038* |
| Psychological variables: | ||||
| Somatosensory amplification | 0.233 | 0.167 | 1.396 | 0.167 |
| Trait anxiety | –0.215 | 0.227 | –0.948 | 0.346 |
| Trait depression | –0.217 | 0.218 | –0.995 | 0.323 |
| Behavioural inhibition | –1.344 | 2.051 | –0.655 | 0.514 |
| Behavioural activation | –1.166 | 2.232 | –0.522 | 0.603 |
| Pain catastrophising | –0.129 | 0.092 | –1.403 | 0.165 |
| Experimenter warmth | –0.727 | 2.059 | –0.353 | 0.725 |
| Experimenter competence | –0.563 | 2.499 | –0.225 | 0.822 |
| Day 8: nocebo effect | ||||
| Intercept | –9.215 | 17.887 | –0.515 | 0.608 |
| Expected worsening pre-conditioning (GEEE) | 0.650 | 0.580 | 1.122 | 0.265 |
| Conditioning nocebo effect (VAS rating) | 0.103 | 0.092 | 1.119 | 0.267 |
| Expected worsening on day 1 (GEEE) | –0.325 | 0.565 | –0.574 | 0.567 |
| Nocebo effect on day 1 (VAS rating) | 0.290 | 0.124 | 2.349 | 0.021* |
| Expected worsening on day 8 (GEEE) | –0.154 | 0.516 | –0.298 | 0.766 |
| Psychological variables: | ||||
| Somatosensory amplification | –0.080 | 0.199 | –0.403 | 0.688 |
| Trait anxiety | 0.099 | 0.288 | 0.345 | 0.731 |
| Trait depression | 0.093 | 0.261 | 0.356 | 0.723 |
| Behavioural inhibition | 1.759 | 2.600 | 0.677 | 0.501 |
| Behavioural activation | –1.615 | 2.861 | –0.565 | 0.574 |
| Pain catastrophising | 0.064 | 0.110 | 0.576 | 0.566 |
| Experimenter warmth | 2.569 | 2.687 | 0.956 | 0.342 |
| Experimenter competence | –0.608 | 3.190 | –0.191 | 0.849 |
GEEE, Generic Rating Scale for Previous Treatment Experiences, Treatment Expectations, and Treatment Effect, VAS, visual analogue scale. Rief et al., 2021.
***P<0.001, **P<0.01, *P<0.05.