Content comparison of health-related quality of life instruments for obstructive sleep apnea

Abstract

Background and purpose

Due to the increasing importance of quality of life assessments in obstructive sleep apnea (OSA) patients and due to an increased use of the International Classification of Functioning, Disability and Health (ICF), for comparative purposes it is essential to understand the relationship between health-related quality of life (HRQOL) instruments and the ICF. The purpose of this study was to compare the content covered by OSA-specific instruments using the ICF.

Patients and methods

OSA-specific instruments were identified, including the Calgary Sleep Apnea Quality of Life Index, the Functional Outcomes of Sleep Questionnaire, the Obstructive Sleep Apnea Patient-Oriented Severity Index, and the Quebec Sleep Questionnaire, and linked to the ICF by six health professionals according to standardized guidelines. The degree of agreement between health professionals was calculated by means of the kappa statistic.

Results

A total of 308 concepts were identified and linked to 78 different ICF categories; 35 categories of the component body function, one category of the component body structure, 38 categories of the component activities and participation, and four categories of the component environmental factors. Only contents within the chapters mental functions, mobility and social life were addressed by all instruments. Forty-seven categories were covered by only one instrument.

Conclusion

The ICF proved highly useful for the comparison of HRQOL instruments. This analysis may help researchers and clinicians to choose the most appropriate HRQOL instrument for a specific purpose as well as help to compare study outcomes of studies using different instruments for HRQOL assessment.

Introduction

Obstructive sleep apnea (OSA) is common, affecting up to 5% of the population of the Western world [1], and is associated with excessive daytime somnolence [2], mental and cognitive impairments [3], higher rates of automobile and work-related accidents [4], [5] and an increased cardio- and cerebrovascular morbidity and mortality [6], [7].

OSA is also associated with increased healthcare costs [8], [9] and decreased quality of life (QOL) [10], [11], [12], [13], [14]. QOL is reduced due to excessive daytime sleepiness [15] and a number of other aspects of OSA, such as headaches, abnormal cognitive performance, memory deficits, irritability, erectile dysfunction, depressive symptoms, and impaired social functioning [14], [16]. It is noteworthy that excessive daytime sleepiness shows only a weak correlation with the severity of the sleep apnea when assessed by physiological parameters in the sleep laboratory [17], [18], [19]. Quality of life assessments in OSA patients have become a main focus in statements on sleep apnea published by various organizations [20], [21], [22]. The American Thoracic Society and the American Sleep Disorders Association [20] have reviewed the use and the properties of currently available specific HRQOL instruments and made specific recommendations for research priorities in the assessment of standard and novel measurement tools in sleep apnea. However, neither of the aforementioned organizations has made recommendations regarding the use of specific health-related quality of life (HRQOL) instruments, in part due to insufficient comparative data.

When selecting HRQOL instruments for research or clinical settings, the validity, practicability, and discrimination of the potential HRQOL instruments should be considered and compared. Several reviews deal with the selection of appropriate HRQOL instruments for OSA, mainly by describing their psychometric properties [23], [24], [25]. The first and foremost concern is face and content validity [26], the quantitative testing of which is rarely attempted [27]. This is also true for OSA-specific HRQOL instruments. Thus, a content comparison based on a universally accepted, well-defined, and standardized reference system that allows for a fine-grained exploration and comparison of all contents of the instruments is needed.

The World Health Organization’s (WHO) International Classification of Functioning, Disability and Health (ICF) [28] is a multi-purpose classification developed to provide a common universal language for the description of a wide range of health-related phenomena. Applying the ICF’s well-defined category system as an independent and external reference to represent the contents of measures makes it possible to explore these contents in a comprehensive, standardized and transparent way, and thus helps to facilitate the choice of assessment instruments in all fields of application [29], [30].

The objective of our study was to examine and compare the contents of HRQOL instruments used in OSA, using the ICF as the frame of reference. The specific aims are (1) to identify the most widely used and recommended OSA-specific HRQOL instruments, (2) to examine the contents of the single instruments based on them being linked to the ICF, and (3) to compare the contents of the OSA-specific instruments.