Methods Used to Identify, Test, and Assess Impact on Preferences of Bolt-Ons: A Systematic Review

Abstract

The question of whether additional dimensions should be added to the EQ-5D, so-called bolt-ons, has been researched since the 1990s. Several candidate bolt-ons have been tested. The aim of this systematic review was to provide an overview of EQ-5D bolt-on studies, including the origin of possible suitable bolt-ons, their format, and methods that were used to examine their value. Methods: Studies were identified through database search and reference screening and assessed based on a set of inclusion criteria. All studies that investigated bolt-ons for the EQ-5D were eligible for inclusion. Two reviewers independently extracted information from all included studies on objectives, study design, EQ-5D version used, the investigated bolt-ons, methods used to achieve objectives, and outcomes. Results: Of 308 initially identified studies, 28 studies met the inclusion criteria. Of these studies, 3 identified potentially suitable bolt-on dimensions, 13 investigated the psychometric performance of EQ-5D 1 bolt-on(s), and 6 investigated the impact of the bolt-on on health state preferences. In total, 26 bolt-ons were identified, of which cognition was the most frequently mentioned. A wide variety of bolt-on identification methods, psychometric performance tests, and health state valuation methods were used in the included studies. Conclusion: A range of bolt-on dimensions has been investigated using diverse methods. Guidelines are needed to standardize the wording of the bolt-on dimension and response options, evaluate minimal important gain of the bolt-on, and facilitate quality assessment of bolt-on studies. Subsequently, guidelines will facilitate decision making on whether or not to implement a bolt-on dimension to the EQ-5D.

Sensitivity of the EQ-5D-5L for fatigue and cognitive problems and their added value in Q-fever patients

“…Each dimension is operationalized in one item with five response levels: no problems, slight problems, some problems, severe problems and extreme problems/unable to [ 13 ]. The EQ VAS consists of one question where respondents rate their health state on a scale from 0 (worst imaginable health state) to 100 (best imaginable health state), and is often used to determine to what extent the EQ-5D captures HRQoL [ 17 ].…”

“…Therefore, a fatigue bolt-on might be less sensitive to change in fatigue complaints than de CIS fatigue score. The addition of a cognition dimension to the EQ-5D has been studied more extensively than fatigue, and cognition has in many studies already been applied as an additional dimension of the EQ-5D [17]. However, while often suggested [16,32,33] and also tested for added value [23,24,28,34,[37][38][39][40], the cognition dimension is not an official EQ-5D dimension.…”

“…However, it has been argued that its brevity may limit the sensitivity to change and content validity in some (patient) populations, and therefore limit its’ ability to measure for example long-term consequences of infectious diseases [ 15 , 16 ]. Moreover, the question rises whether certain aspects of health, such as fatigue and cognition, are sufficiently covered by the EQ-5D, or whether they should be added to the EQ-5D [ 17 ]. Especially in patients with infectious disease, who frequently experience persistent fatigue, cognitive problems, or both, it is crucial that the effects of these problems are captured by the HRQoL measurement instrument.…”

Adding a fatigue item to the EQ-5D-5L improves its psychometric performance in the general population

“…Based on these five scores an index with preference interpretation can be calculated by applying weights which have been separately derived. To cover lack of comprehensiveness, the EQ-5D enables the use of 'bolt-on' items [13,14]. A 'bolt-on' is a item (like fatigue or cognition) on a specific health problem or dysfunction that is not included in the original instrument [13].…”

Adapting preference-based utility measures to capture the impact of cancer treatment-related symptoms

“…The points raised were drawn from the literature and the authors’ own knowledge and experiences, but no systematic review of the literature was undertaken. We are not aware of any existing reviews of studies to augment preference-based measures in general, but refer readers to a review of studies of bolt-ons specifically for the EQ-5D [ 63 ]. This commentary paper has focused on oncology, largely due to the importance of treatment-related symptoms when assessing and comparing immuno-oncology therapies.…”