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182 Fundamentals of quality of life measurement
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Abstracts / Sleep Medicine 7 (2006) S1–S127
182 Fundamentals of quality of life measurement Yves Lacasse * Centre de recherche, Centre de pneumologie, Hoˆpital Laval, Institut universitaire de cardiologie et de pneumologie de l’Universite´ Laval, Que., Canada An important goal of the management of patients with sleep apnea is to alleviate symptoms and dysfunction attributable to the disease. Because symptoms are usually poorly correlated with physiological indices measured in laboratory, quality of life should be assessed directly. The concept of ‘‘quality of life’’ usually refers to the patients’ perception of performance in at least one of four important domains: (1) somatic sensation; (2) physical function, (3) emotional state, and (4) social interaction. The term ‘‘health-related quality of life’’ is often used when widely valued aspects of life not directly related to health, such as income and freedom, are not considered. In clinical studies, the selection of quality-of-life questionnaires must be guided by the investigators’ objectives. Discriminative questionnaires distinguish between groups of patients and are most often used to describe study populations. Discriminative questionnaires must have validity (which refers to whether the instrument is measuring what it claims to measure) and reliability (the ability of the instrument to consistently discriminate between more and less affected patients). Evaluative questionnaires measure change over time. Responsiveness (i.e., the ability of an evaluative instrument to detect real change, even when it is small) is a necessary property for evaluative instruments. For a discriminative instrument, a score is interpretable when it tells to the reader whether the difference between two patients’ function is negligible, small, moderate, or large. For an evaluative instrument, a score is interpretable when it tells to the reader whether a particular change in score represents a small, moderate, or large clinical improvement or deterioration. Clinicians and policymakers are more and more recognizing the importance of measuring health-related quality of life to inform patient management and policy decisions. A clear understanding of the fundamentals of quality-of-life measurement is essential. doi:10.1016/j.sleep.2006.07.086
183 Assessment of quality of life in sleep apnea Jean-Paul Janssens * Division of Pulmonary Diseases, Geneva University Hospital, 1211 Geneva 14, Switzerland Obstructive or central apnea both lead to recurrent arousals from sleep, oxygen desaturations, and daytime sleepiness and fatigue. Both have an adverse impact on
mood, functional status, vigilance, and quality of life [1– 4]. For patients with obstructive sleep apnea, nasal continuous positive airway pressure (nCPAP) has been shown to improve quality of life (QoL) in randomized trials and in a recent Cochrane meta-analysis [5]. Evaluating and quantifying QoL in sleep apnea relies on the assessment of specific and relevant symptoms (i.e., subjective measurement of daytime sleepiness (Epworth Sleepiness Scale) or quantification of mood disturbances (Hospital Anxiety and Depression Scale) [6]), on the use of generic QoL questionnaires (such as the Short Form-36 (SF-36) [7] or the Nottingham Health Profile (NHP) [8]), or disease-specific questionnaires (such as the Calgary Sleep Apnea Index [9], or the Quebec Sleep Questionnaire) [10]. Health-related quality of life (HRQL) questionnaires are divided into domains, which focus on a particular aspect of disease-related symptoms, or every day life, each domain including a certain number of items. Scoring usually requires the use of ponderation coefficients which take into account the relative relevance or ‘‘weight’’ of specific items for the patient. The development of a HRQL questionnaire requires a validation process to determine its validity, reliability, sensitivity, and responsiveness [9,10]. An HRQL instrument is considered valid if it measures what it claims to measure. Validity is sometimes difficult to assess because of the difficulty in establishing a ‘‘gold standard’’; items of an HRQL instrument are expected to correlate with indicators of disease severity, and previously validated scales. Reliability is an important item since it determines the threshold above which a change in HRQL may be considered clinically relevant: this includes test–retest reproducibility, inter-observer reproducibility, and internal consistency (usually assessed by measuring Chronbach’s reliability coefficient a). Internal consistency is important for the clinician because low values preclude the use of a questionnaire for individual patients, while high values (i.e., a P 0.95) allow the use of a questionnaire in the follow-up of individuals [11]. Conversely, high values may indicate redundancy in items included in the questionnaire. Responsiveness and sensitivity are key features for HRQL instruments: responsiveness is the measure of the association between a change in QoL, and the HRQL score, after inducing a change in a variable expected to influence QoL. Sensitivity to change is also central to the choice of an HRQL instrument and can be markedly influenced by the so called ‘‘floor’’ or ‘‘ceiling’’ effects. Last but not least, for any HRQL score, the knowledge of its minimal clinically important difference (MCID) is mandatory for determining if any measured change is not only statistically significant but clinically meaningful and relevant [12,13]. The use of generic questionnaires such as the SF-36 or the NHP is interesting because it assesses wide areas of health-related quality of life [14]. These questionnaires
Abstracts / Sleep Medicine 7 (2006) S1–S127
182 Fundamentals of quality of life measurement Yves Lacasse * Centre de recherche, Centre de pneumologie, Hoˆpital Laval, Institut universitaire de cardiologie et de pneumologie de l’Universite´ Laval, Que., Canada An important goal of the management of patients with sleep apnea is to alleviate symptoms and dysfunction attributable to the disease. Because symptoms are usually poorly correlated with physiological indices measured in laboratory, quality of life should be assessed directly. The concept of ‘‘quality of life’’ usually refers to the patients’ perception of performance in at least one of four important domains: (1) somatic sensation; (2) physical function, (3) emotional state, and (4) social interaction. The term ‘‘health-related quality of life’’ is often used when widely valued aspects of life not directly related to health, such as income and freedom, are not considered. In clinical studies, the selection of quality-of-life questionnaires must be guided by the investigators’ objectives. Discriminative questionnaires distinguish between groups of patients and are most often used to describe study populations. Discriminative questionnaires must have validity (which refers to whether the instrument is measuring what it claims to measure) and reliability (the ability of the instrument to consistently discriminate between more and less affected patients). Evaluative questionnaires measure change over time. Responsiveness (i.e., the ability of an evaluative instrument to detect real change, even when it is small) is a necessary property for evaluative instruments. For a discriminative instrument, a score is interpretable when it tells to the reader whether the difference between two patients’ function is negligible, small, moderate, or large. For an evaluative instrument, a score is interpretable when it tells to the reader whether a particular change in score represents a small, moderate, or large clinical improvement or deterioration. Clinicians and policymakers are more and more recognizing the importance of measuring health-related quality of life to inform patient management and policy decisions. A clear understanding of the fundamentals of quality-of-life measurement is essential. doi:10.1016/j.sleep.2006.07.086
183 Assessment of quality of life in sleep apnea Jean-Paul Janssens * Division of Pulmonary Diseases, Geneva University Hospital, 1211 Geneva 14, Switzerland Obstructive or central apnea both lead to recurrent arousals from sleep, oxygen desaturations, and daytime sleepiness and fatigue. Both have an adverse impact on
mood, functional status, vigilance, and quality of life [1– 4]. For patients with obstructive sleep apnea, nasal continuous positive airway pressure (nCPAP) has been shown to improve quality of life (QoL) in randomized trials and in a recent Cochrane meta-analysis [5]. Evaluating and quantifying QoL in sleep apnea relies on the assessment of specific and relevant symptoms (i.e., subjective measurement of daytime sleepiness (Epworth Sleepiness Scale) or quantification of mood disturbances (Hospital Anxiety and Depression Scale) [6]), on the use of generic QoL questionnaires (such as the Short Form-36 (SF-36) [7] or the Nottingham Health Profile (NHP) [8]), or disease-specific questionnaires (such as the Calgary Sleep Apnea Index [9], or the Quebec Sleep Questionnaire) [10]. Health-related quality of life (HRQL) questionnaires are divided into domains, which focus on a particular aspect of disease-related symptoms, or every day life, each domain including a certain number of items. Scoring usually requires the use of ponderation coefficients which take into account the relative relevance or ‘‘weight’’ of specific items for the patient. The development of a HRQL questionnaire requires a validation process to determine its validity, reliability, sensitivity, and responsiveness [9,10]. An HRQL instrument is considered valid if it measures what it claims to measure. Validity is sometimes difficult to assess because of the difficulty in establishing a ‘‘gold standard’’; items of an HRQL instrument are expected to correlate with indicators of disease severity, and previously validated scales. Reliability is an important item since it determines the threshold above which a change in HRQL may be considered clinically relevant: this includes test–retest reproducibility, inter-observer reproducibility, and internal consistency (usually assessed by measuring Chronbach’s reliability coefficient a). Internal consistency is important for the clinician because low values preclude the use of a questionnaire for individual patients, while high values (i.e., a P 0.95) allow the use of a questionnaire in the follow-up of individuals [11]. Conversely, high values may indicate redundancy in items included in the questionnaire. Responsiveness and sensitivity are key features for HRQL instruments: responsiveness is the measure of the association between a change in QoL, and the HRQL score, after inducing a change in a variable expected to influence QoL. Sensitivity to change is also central to the choice of an HRQL instrument and can be markedly influenced by the so called ‘‘floor’’ or ‘‘ceiling’’ effects. Last but not least, for any HRQL score, the knowledge of its minimal clinically important difference (MCID) is mandatory for determining if any measured change is not only statistically significant but clinically meaningful and relevant [12,13]. The use of generic questionnaires such as the SF-36 or the NHP is interesting because it assesses wide areas of health-related quality of life [14]. These questionnaires