56 Subgroup analyses indicated that factors related to the length of learning paradigms or intensity and type of sensory stimuli did not explain the moderate heterogeneity in nocebo effect sizes. This review provides a comprehensive summary of current findings in the field of nocebo research. We have ruled out some factors that were consistently reported in papers and could not explain the variability in results across studies, and we recommended some important directions for the field, such as increased consistency between study designs for inducing nocebo effects, as well as a systematic examination of the effects of different verbal suggestions on magnitudes of learned nocebo effects.
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