Change in Pain Perception in the Low Back and Lower Extremity by Expectation Instructional Set. Change in pain perception in the low back and lower extremity following spinal manipulative therapy (SMT). Positive numbers indicate hypoalgesia, while negative numbers indicate hyperalgesia. A significant interaction was present in the low back suggesting that post SMT pain perception was dependent upon the group to which the participant was randomly assigned. Follow up pairwise comparison indicated a significant increase in pain perception in subjects receiving a negative expectation instructional set. No interaction was observed in the lower extremity of participants; however, a significant main effect occurred suggesting hypoalgesia regardless of group assignment. Error bars represent 1 standard error of the mean (SEM). * indicates a statistically significant change in pain perception in the low back following SMT at p ≤ 0.05.