Chapter 2 – Meta-analysis 49 pain yielded a somewhat larger pooled effect on the magnitude of nocebo responses (k = 13, g = 0.75, 95% CI 0.59 – 0.91) compared to medium pooled effects of electrical pain (k = 7, g = 0.65, 95% CI 0.51 – 0.79) on nocebo responses. For pain studies that used only verbal suggestions, we examined effects of different pain administration methods (k = 4 thermal, k = 5 electrical, k = 2 mechanical) excluding the single studies using laser, cold pressor, hot water bath, pressure, and histamine. Electrical pain yielded slightly larger pooled effect on the magnitude of nocebo responses (k = 5, g = 0.91, 95% CI 0.65 – 1.17) compared to medium effects of thermal (k = 4, g = 0.69, 95% CI 0.21 – 1.16) and mechanical (k = 2, g = 0.60, 95% CI 0.14 – 1.06). For itch studies that used conditioning with verbal suggestions, there were too few studies to analyze (cowhage k = 1, electrical itch k = 2, and histamine k = 1). For itch studies that used only verbal suggestions, there were again too few studies (k = 2 electrical, k = 3 histamine, k = 1 mechanical).
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