Plain Language Summary

What is it about? The EQ-5D is a widely used, brief measure of health-related quality of life, consisting of 5 questions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. This study investigates the development and use of additional cognition questions (called ‘bolt-ons’) for the EQ-5D. Cognition is a relevant aspect of health-related quality of life in some patient populations but is not included among the questions of the EQ-5D. Researchers aimed to address the problem by developing and using cognition bolt-ons. The paper presents a systematic review to summarize existing studies that developed or used cognition bolt-ons for the EQ-5D and to identify existing question wordings for these cognition bolt-ons.

How was the research conducted? The study is based on a systematic literature review, which is a method used to collect and analyze all relevant research on a particular topic. Researchers applied this method by searching electronic databases for studies on cognition bolt-ons for the adult versions of EQ-5D populations aged 16 years or over. They followed strict guidelines to ensure the quality of their review. The identified publications were summarized narratively.

What were the results? The main finding is that there is a growing demand for cognition bolt-ons, with 181 publications identified, covering 137 studies published between 1997 and 2023. Cognition bolt-ons were used in 71 patient populations, most commonly injury, dementia, depression, HIV, schistosomiasis, and stroke. The research revealed 52 different wordings used for cognition bolt-ons, with the most common examples to describe cognition being concentration, memory, and remembering. Cognition bolt-ons have been used in 28 languages across 24 countries. An unexpected finding was that two-thirds of the studies originated from The Netherlands.

Why are the results important? These results are significant for clinicians, researchers and health technology assessment agencies as they highlight the need for standardized bolt-on(s) to ensure consistency in the measurement of cognition alongside the EQ-5D. Health conditions where any area of cognition is impacted could benefit from the use of cognition bolt-ons alongside the EQ-5D.

What are the strengths and weaknesses of this study? A major strength of the study is its comprehensive review of existing literature, providing a clear picture of the current state of cognition bolt-ons. However, a key weakness is the variability in methodological quality among the studies reviewed, and the fact that researchers could not identify the bolt-on wording for all studies despite making every effort to contact the authors of the original studies. Future research could focus on developing a standard for cognition bolt-on and testing its measurement performance across different populations.

This structured review makes the research accessible to patients, healthcare decision makers, and researchers, aiding in understanding the importance of cognition in health assessments and the need for standardized tools in this area.

^{Note: This content was created with assistance from artificial intelligence (AI) and has been reviewed and edited by ISPOR staff. For more information or for inquiries on ISPOR’s AI policy, click here or contact us at info@ispor.org.}