Mean pain scores on a visual analogue scale (VAS) from time point 1 (baseline) to 15 (450 minutes). MA = manual acupuncture, EA = electro-acupuncture, SC = standard care, n = number of valid observations at each time interval. After time interval 6, n < 41 in MA and EA. After time interval 8, n < 41 in SC. The model with interaction was used to identify time intervals when the three groups differed in pain scores on VAS.