80 Chapter 4 be performed. Patients will be considered to be adherent to the smartphone application if they used the application for at least 2/3rd of the duration (i.e., 2 out of 3 week for the “low-risk” profile and 8 out of 12 weeks for the “medium- and high-risk” profile) (35,75). Per-protocol analyses will be performed using LMM with the same 3-level structure, and will be controlled for the same variables as the primary analysis. Economic evaluation An economic evaluation will be performed from the societal and the healthcare perspective and will assess the cost-effectiveness of e-Exercise LBP compared to usual physiotherapy at 12 and 24 months. Identification, measurement and valuation of costs When the societal perspective is applied intervention, healthcare, informal care, unpaid productivity, and paid productivity costs will be included. When the healthcare perspective is applied, only costs accruing to the formal Dutch healthcare sector will be included. The costs of e-Exercise LBP will be estimated using a bottom-up micro-costing approach (76). Information on the patients’ other kinds of resource use will be collected using eight 3-monthly retrospective cost questionnaires with 3-month recall periods. Healthcare utilization, unpaid productivity, and informal care will be valued in accordance with the “Dutch Manual of Costing” (77). Paid productivity losses comprise of absenteeism (i.e., sickness absence) and presenteeism (i.e., reduced productivity while at work). Absenteeism was measured using a modified version of the IMTA Productivity Cost Questionnaire (iPCQ). Absenteeism will be valued in accordance with the “Friction Cost Approach” (FCA), using gender-specific price weights (78,79). Presenteeism will be measured using the “World Health Organization – Work Performance Questionnaire” as well as the “Productivity and Disease Questionnaire”, and valued using gender-specific price weights as well (78–81). Measurement and valuation of health-related quality of life The patients’ health states will be measured using the EuroQol-5D-5L (EQ-5D-5L) (82–85). This questionnaire comprises of five health dimensions, i.e., mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Per health dimension, patients are asked to indicate their severity level. Health states will be converted into utility values using the Dutch tariff (86) and Quality Adjusted Life Years (QALYs) will be estimated using linear interpolation between measurement points. Statistical analyses Missing cost and effect data will be imputed using ‘Multivariate Imputation by Chained Equations’ and the results will be pooled using Rubin’s rules (87). Cost differences (ΔC) and effect differences (ΔE) will be estimated using LMM, and will be corrected for the same baseline variables as the effectiveness analysis. To account for the highly skewed nature of cost data, bias-corrected and accelerated bootstrapping
RkJQdWJsaXNoZXIy MTk4NDMw