Structural Equation Modelling to Identify Psychometric Determinants of Medication Adherence in a Survey of Kidney Dialysis Patients

Abstract

Mark R Marshall,1– 3,* Samantha Curd,4,* Julia Kennedy,4,* Dharni Khatri,4,* Sophia Lee,4,* Krenare Pireva,4,* Olita Taule’alo,4,* Porsche Tiavale-Moore,4,* Martin J Wolley,3,5,6,* Tian M Ma,3,7,* Angela L Kam,3,8,* Jun S Suh,3,* Trudi J Aspden4,* 1School of Medicine, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand; 2Department of Medicine, Tauranga Hospital, Hauora a Toi Bay of Plenty, Tauranga, New Zealand; 3Department of Renal Medicine, Middlemore Hospital, Counties Manukau Health, Auckland, New Zealand; 4School of Pharmacy, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand; 5Endocrine Hypertension Research Centre, University of Queensland Frazer Institute, Greenslopes and Princess Alexandra Hospitals, Brisbane, Queensland, Australia; 6Department of Nephrology, Royal Brisbane and Women’s Hospital, Brisbane, Queensland, Australia; 7Institute for Innovation + Improvement, North Shore Hospital, Auckland, New Zealand; 8Barts Health NHS Trust, London, UK*These authors contributed equally to this workCorrespondence: Mark R Marshall, Tauranga Hospital, Te Whatu Ora Hauora a Toi Bay of Plenty, 29 Cameron Road, Tauranga South, Tauranga, 3112, New Zealand, Tel [phone], Email [email protected]: Medication non-adherence in dialysis patients is associated with increased mortality and higher healthcare costs. We assessed whether medication adherence is influenced by specific psychometric constructs measuring beliefs about the necessity for medication and concerns about them. We also tested whether medication knowledge, health literacy, and illness perceptions influenced this relationship.Patients and Methods: This study is based on data from a cross-sectional in-person questionnaire, administered to a random sample of all adult dialysis patients at a teaching hospital. The main outcome was self-assessed medication adherence (8-Item Morisky Medication Adherence Scale). The predictors were: concerns about medications and necessity for medication (Beliefs About Medication Questionnaire); health literacy; medication knowledge (Medication Knowledge Evaluation Tool); cognitive, emotional, and comprehensibility Illness perceptions (Brief Illness Perception Questionnaire). Path analysis was performed using structural equations in both covariance and variance-based models.Results: Necessity for medication increased (standardized path coefficient [β] 0.30 [95% CI 0.05, 0.54]) and concerns about medication decreased (standardized β − 0.33 [− 0.57, − 0.09]) medication adherence, explaining most of the variance in outcome (r2=0.95). Medication knowledge and cognitive illness perceptions had no effects on medication adherence, either directly or indirectly. Higher health literacy, greater illness comprehension, and a more positive emotional view of their illness had medium-to-large sized effects in increasing medication adherence. These were indirect rather and direct effects mediated by decreases in concerns about medications (standardized β respectively − 0.40 [− 0.63,-0.16], − 0.60 [− 0.85, − 0.34], − 0.33 [− 0.52, − 0.13]).Conclusion: Interventions that reduce patients’ concerns about their medications are likely to improve adherence, rather than interventions that increase patients’ perceived necessity for medication. Improving patients’ general health literacy and facilitating a better understanding and more positive perception of the illness can probably achieve this. Our study is potentially limited by a lack of generalizability outside of the population and setting in which it was conducted.Keywords: medication adherence, surveys and questionnaires, latent class analysis, renal dialysis

Keywords

• medication adherence
• surveys and questionnaires
• latent class analysis
• renal dialysis