Sex differences in pain, fear of pain and placebo analgesia

Abstract

The hypothesis that males are more responsive to placebo treatment than females was tested experimentally in this thesis. The hypothesis was confirmed and the results showed that the sex difference was related to a difference in males’ and females’ stress response after placebo treatment. Placebo responses on pain unpleasantness and the P2 component was found in males, but not in females. The Fear of Pain Questionnaire-III (FPQ-III) and the Fear of Pain Questionnaire-Short Form (FPQ-SF) are two frequently used instruments that measure fear of pain in clinical and healthy samples. The second and third paper of this thesis examined sex differences in FOP, and model fit, reliability, validity and sex neutrality of these two models. It was expected that FOP would be higher in females than in males and that this would be shown as sex differences in overall FPQ-scores, subscale scores and at item level. Furthermore, it was hypothesized that the FPQ-SF would be preferred over the FPQ-III. The second paper uncovered higher fear of severe pain in females than in males, probably due to sex differences in psychological processes, such as fear and anxiety, and interpretation of fear of pain items. The third paper showed that neither the FPQ-III nor the FPQ-SF models had good fit to the data, although the FPQ-SF model was better suited than the FPQ-III overall and across sex subgroups. We therefore suggested adjustment of the present FOP-instruments. Our findings illustrate the importance of developing culture or country specific FOP models.