Fig. 1

Three top panels: Distribution of the SPS measures of healthy subjects, chronic pain patients and surgical patients, respectively. Higher values are associated with higher pain intensity reports. Fourth panel: The item map providing a subject’s expected score to each item as a function of the measure of his pain attitude. Bottom panel: The relationship between raw scores and the pain attitude measures (solid line) and the 95 % confidence interval (dotted lines). The measures of pain attitude are obtained by converting the ordinal total scores on the 18 items into linear measures. For more details, see the main text and the Additional file 2