The placebo effect of vibratory stimulation was studied in 72 patients with chronic pain syndromes in a double-blind crossover trial using a vibrator and a 'placebo unit'. Pain alleviation was reported by 48% of the patients during vibratory stimulation compared with 34% for placebo treatment; statistical significance (p<0.005).
Lundeberg, T., Abrahamsson, P., Bondesson, L., & Haker, E. (1987). Vibratory stimulation compared to placebo in alleviation of pain. Scandinavian Journal of Rehabilitation Medicine, 19(4), 153–158.