Chapter 3 36 construct [3]. Only the RAdMAT is a multidimensional instrument, making it the most suitable instrument for measuring adherence [2]. The RAdMAT, with 16 items and a four-point rating scale, was developed in the athletic training setting and has been examined within the broader physiotherapy setting in patients with shoulder problems [2]. Exploratory factor analysis used by Granquist et al. in their development study [13] revealed that the RAdMAT consists of three subscales, Attendance/participation, Communication and Attitude/effort, which accounted for 58% of the total variance. In addition, a forced one-factor solution showed that the 16 items loaded strongly onto one factor indicating that the RAdMAT with three subscales could be used as a single factor representative of adherence. The RAdMAT had good internal consistency with a Cronbach’s a of 0.90 and discriminated among adherence levels in the athletic training setting [13]. Granquist et al. [13] used the SIRAS to examine construct (convergent) validity and demonstrated strong positive correlations between the three RAdMAT subscales, the entire questionnaire and the SIRAS, ranging from 0.74 to 0.90. A Dutch version of the RAdMAT, the RAdMAT-NL, is available. This version was prepared by a native speaker based on the guidelines of translating questionnaires [14, 15]. The RAdMAT-NL showed a high inter-rater reliability in a sample of patients in a primary physiotherapy setting [16]. Therefore, the RAdMAT-NL seems to be appropriate for quantifying adherence in patients with COPD. Since it is important that the RAdMAT-NL is a multidimensional instrument, it should be explored whether the RAdMAT-NL indeed consists of multiple dimensions. In addition, it should be determined whether the RAdMAT-NL can be used as a single measure of adherence. The aim of this study was 1. to explore the dimensionality (structural validity) and construct validity of the RAdMAT-NL in patients with chronic obstructive pulmonary disease undertaking pulmonary rehabilitation in a primary physiotherapy practice, and 2. to examine whether the RAdMAT-NL can be used as a single measure of adherence. Methods The reporting of this study complies with the Strengthening The Reporting of Observational Studies in Epidemiology (STROBE) checklist for cohort studies. Participants Participants of this prospective study were Dutch/Flemish-speaking patients aged ³ 18 years who were recruited between January 2021 and December 2021 from 53 primary physiotherapy practices, and from the COPD patient organizations from the Netherlands and Belgium. Included were patients with COPD, with airflow limitation
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