Stefan Elbers

55 Evaluating IMPT programmes over time and further refinement in future studies. To provide transparency regarding our procedures and choices, we published all data extraction forms in the online multimedia appendix. Third, the calculation of pre-post effect sizes in meta-analyses is under debate (Cuijpers et al., 2017; Kösters, 2017). We realize that pre-post effects should not be considered as a valid method for demonstrating a treatment effect. However, the current analysis does provide an indication of the change over time of patients' wellbeing on several key outcomes, which is considered particularly useful from a clinician's perspective (Kösters, 2017). Of notice is that the suggested overestimation of effect size has not been observed in large comparison studies (Anglemyer et al., 2014; Benson & Hartz, 2000; Concato et al., 2000). On the contrary, less heterogeneity was found of observational studies compared to RCTs. A possible explanation was that cohorts within case series potentially better represent the population at risk and tailor treatment to specific patients, compared to RCTs with specific inclusion criteria and standardized protocols. Future Directions An opportunity to increase the lifespan and relevance of this systematic review is to develop this study into a living systematic review. The main characteristic of this type of review is that it will be continuously updated when new evidence becomes available (Elliott et al., 2017). In addition, living systematic reviews often include an online platform where datasets and data analysis syntaxes are publicly available, which may decrease duplicate work (Thomas et al., 2017). This helps to decrease the evidence to practice gap, but also to stimulate collaboration and data-sharing (Elliott et al., 2014). Data validation by authors of the included studies, improved analyses techniques as well as semi-automated search and data extraction procedures are among the possibilities of such an initiative (Bannach- Brown et al., 2019; Thomas et al., 2017). The current multimedia appendix has been developed to accommodate future updates, which will facilitate this transition. Conclusions In the past five decades, pain management programmes evolved from attempts to coordinate various disciplines inmanaging chronic pain to comprehensive interdisciplinary multimodal interventions that help patients to optimize their daily life functioning and their overall wellbeing. This study shows that participation in an IMPT programme is associated with considerable improvements in physical and psychological wellbeing that are generally maintained at follow-up. The current study also revealed that despite common roots these programmes show substantial heterogeneity with respect to dose and treatment content, which suggests different viewpoints on how to optimally design an IMPT intervention. To discuss these differences and learn from this variability, we recommend to improve the precision of describing the intervention rationale and to test the proposed mechanisms by