1. De Groot, F., Voogt-Bode, A., Passchier, J. et al., (2011). Headache: the placebo effects in the control groups in randomised controlled trials; an analysis of systematic reviews, Journal of Manipulative and Physiological Therapeutics, 34(5), 297-305. DOI: 10.1016/j.jmpt.2011.04.007.

https://pubmed.ncbi.nlm.nih.gov/21640253/