Effect of placebo acupuncture over no-treatment: A simple model incorporating the placebo and nocebo effects.

Conventionally in controlled trials of drugs or modalities, the placebo and nocebo effects have been determined separately and understood to be the difference between the placebo and no-treatment groups. Recently, the effect of placebo acupuncture over no-treatment was found to be associated with the placebo and nocebo effects together. If these two effects are inseparable in acupuncture treatment, the conventional method of determining placebo and nocebo effects at the trial level will not reflect pure placebo or nocebo effects. Furthermore, if these effects are inseparable, observations about the efficacy of acupuncture will be biased when considering only the placebo effect. A simple mathematical model incorporating both the placebo and nocebo effects will be provided to see how the efficacy of acupuncture is affected.