Comparing Quality of Life Scales in Childhood Epilepsy: What's in the Measures?

Nora Fayed & Elizabeth N. Kerr

Abstract

Appraising the conceptual content of quality of life (QOL) measures relative to a particular study is an important step in content validation. The purpose of our study was to 1) identify childhood epilepsy-specific QOL outcome measures using a systematic review process, and 2) compare those measures based on a broadly defined, international standard of health, the International Classification of Functioning, Health, and Disability (ICF). Usefulness of the ICF for appraising the content of QOL outcome measures was also described.

Method: A review of the literature was conducted to identify QOL measures. Two independent raters assigned an ICF code to each item of each measure using a modified form of published linking rules. ICF codes were then grouped under health components of body functions, body structures, activities and participation, or environmental factors. A comparison of the percentage of ICF components was performed across the measures. Inter-rater reliability of linking was analyzed using Cohen's kappa.

Introduction

Measures of quality of life (QOL) are popular for describing, evaluating, and comparing the experiences of children with epilepsy. They are used by clinicians, researchers, and community-based programs who wish to assess and evaluate the impact of their efforts to improve a child's health and his or her overall life (Ronen, Streiner, & Rosenbaum, 2003). Users of these measures require consistent and valid methods for determining the actual health content of the QOL measures in a manner that is relevant to children and families affected by epilepsy. Quality of life measures in the field of childhood epilepsy seldom report clear definitions of health or quality of life, often stating expert opinion as the basis for content validation. Yet understanding the content of a measure is integral to determining content validity. Norman and Streiner (2008) describe content validity as the compatibility between that which one seeks to measure and the concept of health contained in the QOL tool. Norman and Streiner (2008) also caution that expert opinion may not be sufficient to capture a measure's content validity if the measure is not representative of the intended concept or if theories assumptions or ideas [of health or quality of life] have changed since the development of the measure. Over the last 5-15 years, a shift in the concept of health has impacted upon the way health is defined relative to quality of life (Wilson & Cleary, 1995). Irrespective of a tool's validity or reliability, one must determine the definition of health in tools used to measure quality of life in children with epilepsy prior to selecting the measure for application in hospital or community based settings.

Understanding of a measure's content is important in the field of quality of life where there is ongoing ambiguity on the part of measurement developers and users alike as to what constitutes a quality of life measure versus a health-status measure. Description of the difference between such measurement approaches has been elucidated by various authors (Bradley, 2001; Cieza & Stucki, 2008; Livingston, Rosenbaum, Russel, & Palisano, 2007). The World Health Organization (1998) defines quality of life as an individual's perception of his/her position in life, while Raphael, Brown, Renwick and Rootman, (1996) describe it as the extent to which an individual enjoys the possibility of his or her life. The implications to the measurement process are such that in order to measure quality of life, one must determine a person's perception or ideas about areas of importance in his or her life with only one of these areas of life being health. Health-status measurement on the other hand might measure similar areas as quality of life including psychological, physical and environmental health but determines only the extent to which the person is experiencing good health or bad health according to these areas. Regardless of whether the approach to measurement is based in health-status or quality of life, it is an essential minimum to determine the definition of health contained in the measures using criteria that are sufficiently multi-dimensional to span both concepts and sufficiently standardized to serve as a basis for comparison.

The International Classification of Functioning, Disability and Health (ICF) provides a guide for comparing the health content of different measures if a broad biopsychosocial definition is intended as the purpose to which the QOL tool will apply. The ICF framework is intended to describe health according individuals' functional capacity within a certain environment as opposed to measuring levels of impairment or physiological dysfunction consistent with a medical model (WHO, 2001). Separate from the framework, the ICF classification can be used to delineate health content through a coding process that employs the several ICF categories. Previous studies using the ICF have assisted researchers to select appropriate outcome measures based on content when the psychometric properties of a measure are appraised by other methods (Stucki et al., 2006; Ceiza & Stucki, 2005). The ICF is divided into components called body function, body structures, activities and participation, and environment. Body function classifies physiological and psychological functions of body systems, body structures classifies anatomical parts of the body such as organs, limbs and their components, activities classifies the execution of tasks or actions while participation classifies the task or action for involvement in life situations. Finally environment classifies the physical, social and attitudinal environment in which people live and conduct their lives (WHO, 2001).

To our knowledge, published reviews of quality of life measures specific to childhood epilepsy have focused on the psychometric properties of a measure (Cowan & Baker, 2004) without focusing on the content of the measure or require revision to include new measures (Carpay & Arts, 1996). No studies have appraised the content of epilepsy specific measures for children. A study which systematically assesses the specific constructs within declared quality of life measures will assist potential users to establish their content validity relative to a particular research or clinical purpose.

The purpose of this study was to conduct a systematic evaluation of the content of childhood-epilepsy specific measures that are described as quality of life tools by evaluating the representativeness of their items relative to the ICF classification.

Methods

Article Identification

A systematic review was conducted to identify QOL measures that were specific to childhood or adolescent epilepsy over the last ten years. We employed a strategy for the search of the literature on Ovid Medline using the keywords epilepsy and quality of life to identify papers published between 1997 and February 2007. The search criterion was limited to articles published in English and confined to children and adolescents aged 0 to 18. This search generated a list of 439 articles. The abstract of each article was reviewed to identify any outcome measures employed or developed in each study. If the outcome measure was not clearly identified from the abstract, the article was accessed and the method section reviewed. Outcome measures were included if they were created for the purpose of measuring quality of life or health-related quality of life with child or adolescent epilepsy as the primary focus area. Measures were excluded if they were focused on specific health domains (such as impairment or activity of daily living) as opposed to quality of life or health-related quality of life or if the measure was validated on an adult sample. For instance the Hague Restrictions in Childhood Epilepsy Scales (Carpay et al., 1997) was omitted due to its focus on activity limitations and participation restrictions. The Impact of Pediatric Epilepsy Scales (Camfield, Breau, & Camfield, 2001) was also omitted because it was the previous version of the Impact of Child Neurological Disability (ICND) (Camfield, Breau, & Camfield, 2003) measure that has since been updated and did meet the inclusion criteria. This resulted in eight measures being selected for review.

Linking Outcomes to the ICF Scheme

The ICF classification scheme represents a variety of health and health-related states that can be accessed on line at http://apps.who.int/classifications/icfbrowser/ in at least six languages. There is little information within the ICF document directing researchers on how to link the content from measures to the ICF codes. The Cieza et al. (2005) ICF linking rules provide guidance on linking content from measures to the ICF and were employed with slight modification. We modified the linking process by assigning one code per item on a questionnaire instead of reducing each questionnaire item into the recommended meaningful units. We identified the dominant concept within the item prior to assigning the concept a specific ICF code. The exception to this rule was that open-ended questions within a measure such as: Is there anything else you wish to tell us about your child's health? were not linked to the ICF. The first letter of the code represented the ICF component of body functions (b) or structures (s), activities and participation (d), or environment (e). The following digits of the code were numeric. For example, item 13 from the Impact of Child Illness Scale (ICI) (Hoare, Mann, & Dunn, 2000): "My child may not find a job when he leaves school" was linked to the code d845 acquiring, keeping and terminating a job in the activities and participation domain of the ICF (see Figure 1). Thus, a measure with fifteen items or questions generates an output of fifteen codes representing the extent to which ICF health determinants such as body functions, body structures, activities and participation, and environmental factors embody the content of the QOL measure.

Figure 1: Linking the Impact of Child Illness Questionnaire item 13 using the ICF

Items that were not easily coded using the previous description were also linked to the ICF using the Cieza et al., (2005) criteria. According to these rules, concepts from an item on an outcome measure that were conceptually part of the ICF yet not easily linked to a specific code were given the code not definable (nd). Concepts such as 'general quality of life', and 'overall mental and physical health' were also assigned the code nd. Items representing personal factors were coded pf and items representing concepts not included in the ICF were coded nc.

Following completion of the linking process, the codes were analyzed for their distribution across ICF categories. This provided a determination of which categories of health were emphasized in each measure.

Coding Assessors

According to an iterative process, two assessors, an occupational therapist and a neuropsychologist familiar with the ICF classification scheme met to review Cieza et al., (2005) linking criteria and rules as well as the modification of the rules such that each item within a measure was the unit of analysis for coding. Two sample items were jointly coded from an excluded measure. Interpretation of linking rules was discussed and clarified. Following this step, the assessors coded all the items from each outcome independently. They then met to discuss any discrepancies in the linking process and decide on a code for the purpose of reaching consensus on the final appropriate code for each dominant concept in an item. Since consensus was achieved for each code, a third party was not required to settle disagreements.

The inter-rater reliability from previous linking reports for generic childhood-based functional measures using kappa coefficients has demonstrated that the level of reliability varies depending on the concepts that are coded by the ICF (Stucki et al., 2006; Ogonowski, Kronk, Rice, & Feldman, 2004). In our study, the reliability of the coding process was analysed between assessors using Cohen's kappa. Ultimately, a consensus approach was used to generate the final list of codes presented in our results.

Results

Reliability of Coding

An analysis of coding agreement between assessors on the ICF appears consistent with previously reported reliability performed by investigators who were not developers of the linking rules (Ogonowski et al., 2004). Our between-assessor comparison was moderately reliable (kappa (k) = 0.56). The agreement between each assessor and the final consensus list of codes was high: the kappas were 0.74 for the occupational therapy assessor and the final list, and 0.68 for the neuropsychologist and the final list.

Outcomes Included

Eight epilepsy-specific outcome measures meeting our criteria were identified from the retrieved studies. These measures are summarized in Table I.

Categories Represented: In total, 443 items were linked to the ICF. Overall the body function domain of the ICF represented 44% of the items across measures followed by 25% in the activity and participation, 18% of codes were not defined, and 8% were represented by the environment domain. The body function section of the ICF was the domain of health most heavily represented in five of eight QOL measures included (Table 2). Body function was represented as one of the top two categories represented by the ICF in all the measures included in the study (Table 2). The body structures (s), not covered (nc), and personal factors (pf) codes were not displayed in the tables since they involved a negligible percentage of values within the measures.

Table 2: Percentage of codes within each ICF category

*Percentages may not sum exactly to 100, nc - not covered codes, s - body structures and pf - personal factors are not displayed due to their negligible impact on the final list of codes

b - represents body functions codes

d - represents activity and participation codes

e - represents environment codes

nd - represents codes not defined

Individual Measures: Two measures, the Health-Related Quality of Life in Children with Epilepsy (Ronen, Streiner, Rosenbaum, & Canadian Paediatric Epilepsy Network, 2003) and the Quality of Life in Paediatric Epilepsy Scale (QOLPES) (Arunkumar, Wyllie, Kotagal, Ong, & Gilliam, 2000) demonstrated a relatively high percentage of environment codes (25-40%) as the dominant concept for the items within their questionnaires (Table 2). These measures also used feedback from children with epilepsy as the initial source of content development for their measure prior to employing expert consensus or literature review. The Epilepsy in Learning Disabilities and Quality of Life (ELDQL) questionnaire (Buck, Smith, Appleton, Baker, & Jacoby, 2007) displayed an exception to this relationship. The ELDQL tool used patient feedback as a primary source of content (Buck et al., 2007) yet the majority of their items were classified in the body function component. Their content was however based on parent interviews only. Measures such as the QOLIE-AD-48 (Cramer et al, 1999), the QOLCE (Sabaz et al., 2000), and the ICND (Camfield, Breau, & Camfield, 2003) were measures with the lowest percentage of environment codes and employed either expert panels or did not fully describe the development of their content. The development of content in the DISABKIDS measure was described in detail (Baars et al., 2005) (Table 1, see appendix) and emphasized body function as dominant concept in the measure. It was however evaluated in its condition-specific form in order to meet the study's inclusion criteria and the generic-portion of the measure, KIDSCREEN, was omitted (Baars et al., 2005). Thus only a part of that QOL measure was linked to the ICF for this analysis, which may account for the dominance of body function codes.

Codes not covered: Of the codes not covered (nc), four main concepts were identified that were represented in an outcome measure but not represented by the ICF. These included: social isolation, safety, death, and injury. The number of codes identified as nc under each of these concepts is identified in Figure 2.

Codes not defined: The not-defined codes, nd, represented items within measures that were contained within the ICF, yet not easily mapped onto a specific code. These constituted 9-28 percent of the codes within each measure.

Figure 2: Concepts found in the QOL measures, not covered by the ICF

Discussion

The purpose of this study was to appraise the health content in quality of life and health-related quality of life measures available for use in childhood epilepsy based on the ICF. Analysis of a measure's content is a vital aspect of establishing content validity prior to instrument selection. The ICF classification provided a standard reference tool for comparing the content of the measures in a systematic way. The method of content appraisal chosen carried certain limitations. The analysis focused on the content in a descriptive manner while neglecting the perspective of the questionnaire and its items. Our results do not distinguish between a health-status measure and a quality of life measure but merely delineate health content according to a broad health perspective. Content analysis methods designed specifically for appraising questionnaires would provide a greater depth of information for measurement selection if they could describe the approach or perspective of measurement (e.g., health status versus quality of life) in addition to content.

The level of initial agreement between the two ICF linkers in this study was moderate, which has been previously reported in studies where information has been linked to the ICF (Kukafka, Bales, Burkhardt, & Friedman, 2006; Ogonowski et al., 2004). In a purely quantitative study, this might be perceived as a limitation. The focus of the linking process as recommended by Cieza et al., 2005 was iterative, and therefore aimed at reaching a valid consensus while representing a variety of interdisciplinary perspectives. We have indicated a finding that agreement between the assessors and the final consensus list of codes is more relevant to report than the between-assessor agreement based on the notion that each assessor contributed more to the final list of codes then to agreement with each other. Using a methodology that combines qualitative and qualitative elements, representativeness in the final consensus list can sometimes only be reached at the expense of initial agreement.

Our main findings carry face validity to researchers who have observed a dominance of body function or impairment related concepts in tools that claim to focus on a concept as multidimensional as quality of life. This emphasis on body function in measures that are titled as quality of life tools in childhood epilepsy is consistent with a review of constructs pertaining to knowledge gaps in the area of epilepsy care (Berto, 2002). The review found that the impact of epilepsy on quality life could not be determined in the absence of information relating to activities and participation and that such information was under-measured and under-studied in the field. Both our results and Berto's (2002) results are reflective of a need for epilepsy measurement activities to more adequately match broader definitions of health in order to meet the needs of describing the impact of childhood epilepsy in the lives of children.

We found that measures developed by consulting children as the starting point for content more strongly emphasize environment aspects of health. This finding compliments the results of qualitative studies that emphasize the importance of environmental health determinants such as the attitudes and perceptions of others on quality of life for children with epilepsy (Elliott, Lach, & Smith, 2005; Hightower, Carmon, & Minick, 2002). The combined analysis of all the items in all the measures indicates that quality of life tools available for children with epilepsy should consider integrating a greater proportion of environment determinants of health or disability relative to body functions in future measurement development. Two QOL tools, the 'Health Related Quality of Life in Children with Epilepsy' tool (Ronen et al., 2003) and the Quality of Life in Pediatric Epilepsy Scale QOLPES (Arunkumar et al., 2000) displayed content that emphasized the environment portion of the ICF. Concepts in the environment domain from the ICF that apply to children with epilepsy include: attitudes, social supports, and health services and systems available to the child. These concepts are all important to quality of life and should be evaluated in this group and thus considered in future revisions of outcome measures. The inclusion of environment determinants of health is also essential to measurement that is theoretically guided by contemporary models of health and disability (Wilson & Cleary 1995; WHO, 2001). Thus inclusion of a greater proportion of environment content in quality of life measures meets targets of measurement that are representative of what is important to children as well as being conceptually-driven.

There are concepts emerging from our analysis relevant to childhood epilepsy that are not identified in the ICF. Death, injury, and isolation are viewed as negative terms and thus do not fit the objective of the ICF to frame health states in neutral language. However, the concept of safety emerged from the measures included in the study and was also not covered by the ICF. While safety is important for children with epilepsy, it also applies to a number of other populations and age groups. Thus future revisions of the ICF might consider safety as a construct worth examining for inclusion in the classification.

Conclusion

Analysis of a measure's content is a vital aspect of instrument selection and the ICF classification provided a basis for such a comparison. This study provides systematically-derived information about content that can be used to establish content validity by clinician and community-based groups who wish to match measurement tools to their intended purposes. This study also demonstrated the application of determining content appraisal of measures using the ICF classification while calling for further development in methods so that one can distinguish the perspectives represented by measures (e.g., quality of life vs health status) in addition to the content of measures.

The findings also demonstrated a bias of measurement content towards impairment-based concepts that were classified as body function by the ICF to the exclusion of content about attitudes and social support classified as environment by the ICF. Conversely, the tools that involved children more heavily in the content development phases of their measures had more concepts classified as environment by the ICF. This association between responses given by children from qualitative research in the content development of a measure and the proportion of environment-based content eventually found in the measure, implies that content about friends and the attitudes of others is important to include in a measure that truly represents their quality of life.

This review was not intended to appraise psychometric properties of epilepsy-specific QOL measures aside from content validity. Prior to selecting an appropriate measure, reviews that focus on psychometrics (Cowan & Baker, 2004; Baker, Hesdon, & Marson, 2000; Carpay & Arts, 1996) should be consulted in addition to the results of this paper. We do however recommend that these findings be consulted prior to establishing the content validity of QOL measures relative to a particular purpose in a clinical or community-based setting.

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Table 1: Basic Characteristics of the QOL Outcomes Identified

*It is recommended that the DISABKIDS be used as an-epilepsy specific module in conjunction with KIDSCREEN, a generic measure of health-related quality of life measure. The content development of DISABKIDS was described in conjunction with KIDSCREEN

Table 3: The most frequently represented ICF component in each measure

Acknowledgements

The first author of this study wishes to acknowledge the continuing support provided by the Canadian Institutes of Health Research Strategic Training Fellowship, McMaster University, and the Quality of Life program. We also acknowledge the editing support of Drs. Peter Rosenbaum and Joy MacDermid.

Author's Contributions:

Nora Fayed completed the review of measures, devised the study's purpose, researched the methodology and drafted the manuscript.

Elizabeth Kerr learned the methodology, applied it to the measures identified and reviewed, edited and assisted with revisions of the manuscript.

Contributors:

Corresponding Author: Nora Fayed, McMaster University, School of Rehabilitation Science, 1400 Main St. W. IAHS 402 Hamilton, ON. Canada, L8S 1C7

Email: fayedn@mcmaster.ca

Elizabeth N. Kerr: Department of Psychology, The Hospital for Sick Children 555 University Avenue, Toronto, ON, Canada, M5G 1X8

Authors' Biographies:

Nora Fayed is an occupational therapist and a PhD student in the Department of Rehabilitation Science at McMaster University in Hamilton, Canada. Originally from Toronto, Canada, she received her BSc. in Kinesiology from the University of Waterloo in 2001 and her MSc. in Occupational Therapy from the University of Western Ontario in 2003. Ms. Fayed is interested in the methodology and applications of ICF linking as well as the relationships between the ICF perspective of health and disability and various models of quality of life in children with epilepsy.

Elizabeth Kerr has been a clinical neuropsychologist at the Hospital for Sick Children in Toronto, Canada, since 1995. She is an associate scientific staff member with the Division of Neurology at SickKids Hospital in Toronto, and holds an adjunct clinical academic appointment with the Department of Paediatrics at the University of Toronto. Dr. Kerr's major research activities focus on neurocognitive and behavioural outcomes in medically intractable epilepsy and genetic conditions.

International Journal of Disability, Community & Rehabilitation
Volume 8, No. 3
www.ijdcr.ca
ISSN 1703-3381