Based on the analysis of results from sham surgery, Ko et al., using brain imaging, claim to be able to identify PwP who are particularly susceptible to the placebo effect.

"Approximately 35% of the participants would fall into this category".

Identifying such people and excluding them from the clinical trial

"substantially lowers the number of randomized participants needed to demonstrate treatment efficacy ... [Here it] resulted in a net reduction in sample size of over 56%."

For the sham responders, 6 months after sham surgery, and still unblinded, the size of the effect was a reduction in the UPDRS motor score of approximately 8 (note a decrease in UPDRS score is good) as compared to an average baseline score of 39.4.

Turning this finding on its head, it seems to me that it makes it easier to target placebo/therebo therapies at those who are most likely to benefit.

Reference

[1] "Network modulation following sham surgery in Parkinson’s disease"
Ji Hyun Ko1, Andrew Feigin1, Paul J. Mattis1, Chris C. Tang1, Yilong Ma1, Vijay Dhawan1, Matthew J. During2, Michael G. Kaplitt3 and David Eidelberg1
J Clin Invest. doi:10.1172/JCI75073, 2014
http://www.jci.org/articles/view/75073

John