Stefan Elbers

188 Chapter 7 Twelve-Item Short Form Health Survey. The 12-item short-form health survey (SF-12) contains 12 multiple choice items that cover 8 health status domains. Raw item scores are combined and transformed into two summary scores: a physical and a mental component score (Cunillera et al., 2010). Higher scores reflect better mental or physical functioning. The SF-12 is considered valid and reliable and has been previously used in patients with chronic pain (Aaronson et al., 1998; Hoffman & Dukes, 2008; Luo et al., 2003; Picavet & Hoeymans, 2004). Pain Self-Efficacy Questionnaire. The Pain Self-Efficacy Questionnaire (PSEQ) assesses self-efficacy beliefs regarding daily life goals in the context of chronic pain (Nicholas, 1989; Nicholas, 2007). The questionnaire includes 10 items that ask a patient to indicate the degree of confidence to perform specific activities (e.g., socializing with friends) despite the pain. Responses are obtained using a Likert scale, ranging from 0 (not confident at all) to 6 (completely confident). The sum of individual scores indicates the total pain self-efficacy. A study on the psychometric properties in a Dutch population of patients with chronic pain demonstrated that the PSEQ is an internally consistent unidimensional instrument (Van Der Maas et al., 2012). Brief Illness Perceptions Questionnaire Dutch Language Version. The Dutch language version of the Illness Perception Questionnaire (IPQ-K [DLV]) measures how patients evaluate their current health condition with respect to 8 areas of cognitive perception (Leysen et al., 2015). The questionnaire includes 9 items, with 8 items covering a different cognitive area (e.g., controllability) with a Likert-scale response option, ranging from 0 (absolutely no control) to 10 (extreme amount of control). The last item requires the patient to list the 3 most important causes for their current condition. A systematic review on the clinimetric properties of the IPQ-K (DLV) concluded that the questionnaire is appropriate to explore the illness beliefs of various patient groups, including acceptable test-retest reliability. However, the smallest detectable change of 42 (on a maximum of 80 points) implies that the use of an IPQ sum score to detect individual changes is not recommended (Leysen et al., 2015). Therefore, we will not use the sum score but instead evaluate each item separately (de Raaij et al., 2012). Pain Intensity. We will measure current pain intensity on a numerical rating scale ranging from 0 (no pain) to 10 (worst pain imaginable). Global Perceived Effect. The global perceived effect (GPE) evaluates to what extent the patient’s current condition has improved or worsened compared to the period prior to the treatment progamme. Patients respond with a 5-point Likert scale, ranging from