Exploration of the psychometric properties of the novel General Medication Adherence Scale (GMAS) for chronic illness patients

Abstract

Objective

Many related scales have been developed and applied to measure patients’ medication adherence, but the research on the psychometric characteristics of the scale still requires further studies. This study aims to provide further validation of the GMAS scale by using Rasch analysis and to make targeted recommendations for scale improvement.

Methods

This is a cross-sectional study using secondary data. 312 Chinese adult patients were recruited from two tertiary hospitals and one community health service center in Tianjin to complete a questionnaire containing the GMAS, from January to June 2020. Participants included to have at least one chronic condition and also have been on medication for more than 3 months, but excluded patients with major life-threatening illnesses (e.g. heart failure, cancer), cognitive impairments preventing clear expression and significant communication difficulties. Rasch analysis was used to explore the psychometric properties of the GMAS scale. Key indicators including unidimensionality, validity and reliability, differential item functioning and degree of fit with Rasch model are validated.

Results

After fitting the Rasch model for the first time, 56 samples poorly fitting the model were deleted. The remaining 256 samples were used for Rasch analysis. The results show that GMAS can fit the Rasch model well, which proves that the scale has favourable psychometric characteristics. But some items had differential item functioning in whether patients have comorbidities.

Conclusion

The GMAS was found to be useful as a screening tool for patients’ medication adherence problems reported, except some issues to be addressed for further improvement of the scale.

Keywords:

• Rasch analysis
• chronic illness
• medication adherence
• validation studies as topic
• reliability

Transparency

Declaration of funding

The research was supported by [the National Natural Science Foundation of China] grant number [71904143].

Declaration of financial/other relationships

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Author contributions

QZ, XYZ, and LW contributed to conception and design of the study. YW and XXW organized the database. XXM performed the statistical analysis. XXM wrote the first draft of the manuscript. SYL, QYL and DYL wrote sections of the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.

Acknowledgements

The authors would like to thank all the patients as well as their family members who willingly agreed to participate in this study. Thanks to Dr. Atta Abbas Naqvi for authorizing the scale.

Data availability statement 

Data available on request from the authors. The data that support the findings of this study are available from the corresponding author, [Qing Zhang], upon reasonable request.

Ethics statement

This study was approved by the Ethics Committee of Tianjin Medical University with the ID number of Code TmuhMEC2019002. All the methods were carried out in accordance with relevant guidelines and regulations. Meanwhile, informed consent was obtained from all subjects and/or their legal guardian(s).