Chapter 3 48 Granquist et al. suggested the RAdMAT could be used as a single score but did not statistically show this [13]. The Rasch analysis in our study showed that the RAdMAT-NL can be used as a single score for adherence without the communication items. Rasch model fit statistics indicated unidimensionality for both Participation and Communication dimensions. Only Participation item 14 had infit and outfit statistics slightly above the 1.5 cut-off, interfering with unidimensionality but not degrading for measurement [32]. The unidimensional Rasch model was rejected for a summed score of all 16 RAdMAT-NL items because of the communication items. Granquist et al. [13] also made their own observation regarding the communication items. They described that two previous studies [33, 34] addressed communication as an important factor for rehabilitation adherence, but that literature does not identify communication as a rehabilitation-adherence behavior [1]. Granquist et al. [13] concluded that athletic trainers likely use other cues/communication and that this should be kept in mind when interpreting the results of adherence. This may have caused the deviation from unidimensionality by the communication items. Also, the communication items showed more variation possibly indicating a wider range of opinions or perspectives among the physiotherapists. Although communication is an important aspect of rehabilitation, the communication items involve the patient's communication only, which is less appropriate for assessment of adherence in a medical rehabilitation setting. Items evaluating the quality of patient-therapist communication are probably more appropriate in a medical rehabilitation setting, where shared decision making is central. Follow-up research should further explore the validity of the RAdMATNL, preferably with a larger sample size, to assess the robustness of the results and especially to further investigate content validity with regard to the formulation of the communication items and whether or not to retain communication items to assess adherence in medical rehabilitation. Construct validity Granquist et al. [13] used the SIRAS to examine convergent validity and demonstrated strong correlations between the RAdMAT and the SIRAS, suggesting the RAdMAT is a valid measure of rehabilitation adherence for use in the context of rehabilitation for injured college athletes [13]. Clark et al. confirmed these results and added the correlation between the RAdMAT and percentage attendance [2]. The results of our study were similar to those of Granquist et al. [13] and of Clark et al. [2] regarding the correlations. Furthermore, this study ratified convergent validity by demonstrating correlations with other adherence measures, including perceived overall adherence, home-based adherence and the change on the FTSST. The overall observed positive correlations confirm that the RAdMAT-NL is associated with attendance to appointments, exercise skills and self-rated adherence which suggests the potential clinical relevance of the RAdMAT-NL.
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