Applying a measurement system analysis approach to dyadic data

Introduction: The Person-Centred Care instrument for outpatient care (PCCoc) is a
36-item patient-reported experience measure with 4 ordered response categories, that aims
to capture the degree of perceived person-centred care (PCC) from a patient perspective
among persons with long-term conditions. The PCCoc is based on a framework that
conceptualises outpatient PCC from lower to higher levels of perceived PCC, from
personalization via shared decision-making to empowerment, where 35 of the PCCoc items
are a part of the framework´s hierarchy. This study investigates to what extent empirical
item responses are consistent with the hierarchical PCCoc conceptual framework among
persons with long-term conditions in outpatient care.

Methods: PCCoc data (322 responses) from persons with long-term psychiatric, cardiological, rheumatological or neurological conditions were analysed. The Rasch measurement
model (RMM) was used to evaluate model fit and the empirical item ordering. Correspondence between the empirical and conceptually expected item hierarchies was assessed
graphically and using the polyserial correlation between RMM derived item locations and
their a-priori expected rank order.

Result: Two items showed clear misfit to the RMM (fit residuals >4.9). The polyserial correlation between empirical item locations and the expected rank order using all
35 PCCoc items was 0.64; after removing the 2 misfitting items it was 0.71. In addition,
subtests (i.e., testlets consisting of a combination of all items belonging to the respective
hierarchical domain) were created to account for any local dependency. Subtest locations
on the hierarchical continuum indicated good correspondence between empirical data and
the conceptual hierarchy, when based on 35 as well as 33 items. Both subtests had a
polyserial correlation of 0.99 between testlet locations and the expected rank order.

Conclusion: The observed correspondence between empirical data and the conceptual
framework indicates that the PCCoc reflects the underlying framework, and therefore can
be a valuable instrument to support targeted PCC-promoting interventions.