Development, psychometric evaluation and validation of a brief measure of emotional preoperative stress (B-MEPS) to predict moderate to intense postoperative acute pain†   W. Caumo, M. Nazare Furtado da Cunha, S. Camey, S. Maris de Jezus Castro, I.L.S. Torres, L. Cadore Stefani  British Journal of Anaesthesia  Volume 117, Issue 5, Pages 642-649 (November 2016) DOI: 10.1093/bja/aew310 Copyright © 2016 The Author(s) Terms and Conditions

Fig 1 The flow of the studies (1, 2, 3). The State-Trait Anxiety Inventory (STAI-S-T) has four answer possibilities: (1) not at all, (2) somewhat, (3) moderately, (4) and very much so, for 13 different items. Trait anxiety presents three answer possibilities: (1) almost never, (2) often and (3) almost always, for 12 different items. The Montgomery-Äsberg Depression Rating Scale (MADRS) contains ten questions ranging from 0 to 6 points. The World Health Organization’s (WHO) SRQ-20 - used to measure minor psychiatric disorders – somatic symptoms, depressive mood, depressive thoughts and decreased energy. Twenty questions require a “yes/no” answer.10 The Future Self-perception Questionnaire (FSPQ) consists of ten simple choice questions addressing the patient’s perceptions of his/her future. Individual scores vary from -2 to +2. 11 38. British Journal of Anaesthesia 2016 117, 642-649DOI: (10.1093/bja/aew310) Copyright © 2016 The Author(s) Terms and Conditions

Fig 2 (A) The lines represent four categories in the original STAI-S scale: (1) not at all, (2) somewhat, (3) moderately, (4) and very much so. (B) Thick lines indicate, from left to right, the location of items of increasing emotional preoperative stress. The IRT psychometric model conceptualizes the measurement scale similar to a ruler (Fig. B). Gradations of the measurement scale are called the items, which are located along the measurement scale according to their stress level. Subjects with a low stress level are situated on the left of the scale, while subjects with a higher stress level are located on the right. For instance, subject A presents with very low preoperative emotional stress because he/she is expected to achieve only three stress items successfully; subject B has an intermediate stress level that should enable him/her to complete approximately half of the items; and subject C has the highest preoperative emotional stress and is expected to complete all the most emotional preoperative stress items. (C) According to IRT the x-axis (horizontal) reflects theta, the ability level (or latent trait level) of the test taker. The y-axis (vertical) reflects the probability of endorsing an item. The curve shows the region where the group of items (B-MEPS) estimates the latent trait of ′preoperative emotional stress′ with greater accuracy. In this case, a preoperative emotional stress level will be determined with high accuracy when it is roughly between 1 and 2 standard deviations of the mean. The item characteristic curve shows the probability of patients positively answering the items according to their emotional stress on a continuum. British Journal of Anaesthesia 2016 117, 642-649DOI: (10.1093/bja/aew310) Copyright © 2016 The Author(s) Terms and Conditions