Latent class analysis of the short and long form of the chronic pain acceptance questionnaire

A substantial literature indicates that pain acceptance is a useful behavioral process in chronic pain rehabilitation. Pain acceptance consists of willingness to experience pain and to engage in important activities even in the presence of pain and is often measured using the Chronic Pain Acceptance Questionnaire (CPAQ). Previous traditional cluster analyses of the 20-item CPAQ identified three patient clusters which differed across measures of patient functioning in meaningful ways. The aims of this study were to replicate the prior study in a new sample, using the more robust method of Latent Class Analysis (LCA), and to compare the cluster structure of the CPAQ and the shorter CPAQ-8. In total, 914 patients with chronic pain completed the CPAQ and a range of measures of psychological and physical function. Patient clusters identified via LCA were then used to compare patients across functional measures. Contrary to previous research, LCA demonstrated that a four-cluster structure was superior to a three cluster. Consistent with previous research, cluster membership based on patterns of pain willingness and activity engagement was significantly associated with specific patterns of psychological and physical function, in line with theoretical predictions. These cluster structures were similar for both CPAQ-20 and 8-items. These results provide further evidence of the relevance of chronic pain acceptance, and a more nuanced understanding of how the components of acceptance are related to function. Perspective: Pain acceptance is important in chronic pain The findings of the present study, which included 914 individuals with chronic pain, provide support for four discrete groups of patients based on levels of acceptance: low, medium, and high, as well as a group that is high in activity engagement and low willingness to have pain. Rovner, Vowles, Gerdle & Gillanders Cluster Analysis of the CPAQ-20 and CPAQ-8 4 These groups appear statistically robust and also differed in predictable ways across measures of functioning. Introduction The concept of acceptance of pain has now gained considerable evidence as to its applicability to chronic pain [e.g. 32; 35]. Pain acceptance is associated with less avoidance, anxiety, depression and healthcare visits and increased work capacity [27; 33]. Interventions that improve acceptance, such as Acceptance and Commitment Therapy [ACT: 19; 35], are effective in lowering psychological and physical disability, improving health, functioning and quality of life [5; 8; 30; 31; 62]. Chronic pain acceptance is typically measured via the Chronic Pain Acceptance Questionnaire [CPAQ: 12; 36]. The CPAQ is sensitive to treatment, psychometrically robust [45], and was developed in line with a “functional contextual” framework to reflect the particular emphasis of ACT on function and consequences of behavior. In addition to strong correlations with a number of key measures of patient functioning, the CPAQ offers an advantage of evaluating adaptive functioning, as opposed to a focus strictly on measuring ‘maladaptive’ functioning (e.g., pain-related distress, anxiety, “catastrophizing”) [29; 37]. The CPAQ consists of two subscales, each assessing different aspects of pain acceptance. The first of these, Activity Engagement (AE), assesses the degree to which respondents report being active with the continuing experience of pain. The second, Pain Willingness (PW), assesses the degree to which respondents report being open to the experience of pain without the need to engage in unsuccessful pain control efforts. Using these two subscales, Vowles, McCracken, & Eccleston [59] performed hierarchical and k-means cluster analyses to investigate if patient subgroups could be Rovner, Vowles, Gerdle & Gillanders Cluster Analysis of the CPAQ-20 and CPAQ-8 5 identified. These analyses indicated the presence of three discrete clusters of patients: high AE and PW (high acceptance), Low AE and PW (low acceptance), and a ‘mixed’ cluster, high in AE and low PW. The Vowles et al. cluster analysis has not been replicated, nor has a cluster analysis been performed using the short form of the CPAQ, the CPAQ-8 [11]. The objectives of the present analyses were to provide an updated analysis of cluster structure of the CPAQ-20 in a new sample of patients using a more advanced and empirically sound cluster analytic approach (Latent Class Analysis) and to evaluate the cluster structure of the CPAQ-8 in comparison to the CPAQ-20. Further, in order to assess the utility of cluster membership, differences in self-reported measures of physical and emotional functioning based on cluster membership were evaluated. Rovner, Vowles, Gerdle & Gillanders Cluster Analysis of the CPAQ-20 and CPAQ-8 6 Methods Participants Over a 25 month period, 1391 patients were referred to the Pain and Rehabilitation Center (PRC) at the University Hospital, Linköping, Sweden, and 914 (66%) patients had complete CPAQ data. The CPAQ was not a compulsory part of the assessment questionnaire battery at that time, explaining the discrepancy between total referrals and current sample. Sociodemographic information and pain characteristics of the patients are summarized in Table 1. [Insert Table 1 about here] These patients, compared to all the patients with chronic pain registered at the Swedish Registry of Pain Rehabilitation [53]were 6 years younger and less educated (only 18.0% had university education while the SQRP reports 25.0%, and 26.4% had only elementary school while the SQRP reports 11.0%). Other than this, this population was similar in educational profile to those described in epidemiological studies and national reports [4; 14; 42] Procedure Data collection Along with most of the pain rehabilitation clinics, the PRC gathers data for the Swedish Quality Registry for Pain Rehabilitation [SQRP: 53] which monitors assessment and outcome of pain rehabilitation clinics in Sweden. The SQRP includes diagnoses as well as descriptive self-report variables of the patient’s background, pain characteristics, and other self-report measures of domains such as depression and anxiety, quality of life and attitudes towards pain. Rovner, Vowles, Gerdle & Gillanders Cluster Analysis of the CPAQ-20 and CPAQ-8 7 Before the first assessment, all patients gave their written informed consent to be registered at the SQRP in accordance with the Declaration of Helsinki. This consent includes consenting for their data to be used in research studies such as the present one. The study was granted ethical clearance by the Regional Ethics Board in Gothenburg (approval #: 815-12). Data of SQRP used in the present study Demographic data included: Sex, years of education, work status, sick leave or insurance/work situation. Pain variables included current pain severity, duration, and frequency, as well as anatomical regions with worst pain (see Table 1).