• Ellen Ricke, Robert Lindeboom, Arie Dijkstra, and Eric W Bakker.
• Department of Social Psychology, University of Groningen, Groningen, the Netherlands.
• Patient Prefer Adher. 2023 Jan 1; 17: 197719871977-1987.

PurposeMeasuring exercise adherence is important in patients with chronic obstructive pulmonary disease (COPD). For this, the Rehabilitation Adherence Measure for Athletic Training (RAdMAT) seems to be a promising instrument, and a Dutch version (RAdMAT-NL) is available. The aim of this study was to explore the dimensionality and construct validity of the RAdMAT-NL in patients with COPD. Secondly, we examined whether the items of the RAdMAT-NL could be summed to a single score.Patients And MethodsThis prospective study included 193 patients with COPD from 53 primary physiotherapy practices in The Netherlands and Belgium. Patients and their physiotherapist provided data including the RAdMAT-NL, at one, two, and three months after inclusion. Horn's parallel analysis and exploratory factor analysis (EFA) were used to assess the dimensionality of the RAdMAT-NL. Fit to the dichotomous Rasch model for measurement was used to confirm the unidimensionality of the extracted RAdMAT-NL subscales and total scale. To evaluate construct validity, Spearman correlations with other indicators of adherence were calculated, including SIRAS score, percentage attendance and change in exercise skills.ResultsEFA identified two dimensions of the RAdMAT-NL, "Participation" (13 items) and "Communication" (3 items), explaining 50.8% of the total variance. Rasch analysis confirmed the unidimensionality of the two dimensions. The unidimensional Rasch model was rejected for a summed score of all 16 RAdMAT-NL items. Medium to large significant positive correlations between the RAdMAT-NL subscale participation and different measures of adherence supported its convergent validity.ConclusionThe RAdMAT-NL exhibited two subscales that fitted the unidimensional Rasch model for objective measurement. Construct validity was supported by convergence with other established measures of adherence.© 2023 Ricke et al.

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