Background A number of studies have computed the minimally important difference (MID) for health-related quality of life instruments. Objective To determine whether there is consistency in the magnitude of MID estimates from different instruments. Methods We conducted a systematic review of the literature to identify studies that computed an MID and contained sufficient information to compute an effect size (ES). Thirty-eight studies fulfilled the criteria, resulting in 62 ESs. Results For all but 6 studies, the MID estimates were close to one half a SD (mean = 0.495, SD = 0.155). There was no consistent relationship with factors such as disease-specific or generic instrument or the number of response options. Negative changes were not associated with larger ESs. Population-based estimation procedures and brief follow-up were associated with smaller ESs, and acute conditions with larger ESs. An explanation for this consistency is that research in psychology has shown that the limit of people's ability to discriminate over a wide range of tasks is approximately 1 part in 7, which is very close to half a SD. Conclusion In most circumstances, the threshold of discrimination for changes in health-related quality of life for chronic diseases appears to be approximately half a SD.

Interpretation of changes in health-related quality of life the remarkable universality of half a standard deviation

Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma

Background: The assessment of asthma control is pivotal to the evaluation of treatment response in individuals and in clinical trials. Previously, asthma control, severity, and exacerbations were defined and assessed in many different ways.Purpose: The Task Force was established to provide recommendations about standardization of outcomes relating to asthma control, severity, and exacerbations in clinical trials and clinical practice, for adults and children aged 6 years or older.Methods: A narrative literature review was conducted to evaluate the measurement properties and strengths/weaknesses of outcome measures relevant to asthma control and exacerbations. The review focused on diary variables, physiologic measurements, composite scores, biomarkers, quality of life questionnaires, and indirect measures.Results: The Task Force developed new definitions for asthma control, severity, and exacerbations, based on current treatment principles and clinical and research relevance. In view of current knowledge ...

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An official American Thoracic Society/European Respiratory Society statement: asthma control and exacerbations: standardizing endpoints for clinical asthma trials and clinical practice.

One can classify ways to establish the interpretability of quality-of-life measures as anchor based or distribution based. Anchor-based measures require an independent standard or anchor that is itself interpretable and at least moderately correlated with the instrument being explored. One can further classify anchor-based approaches into population-focused and individual-focused measures. Population-focused approaches are analogous to construct validation and rely on multiple anchors that frame an individual's response in terms of the entire population (eg, a group of patients with a score of 40 has a mortality of 20%). Anchors for population-based approaches include status on a single item, diagnosis, symptoms, disease severity, and response to treatment. Individual-focused approaches are analogous to criterion validation. These methods, which rely on a single anchor and establish a minimum important difference in change in score, require 2 steps. The first step establishes the smallest change in score that patients consider, on average, to be important (the minimum important difference). The second step estimates the proportion of patients who have achieved that minimum important difference. Anchors for the individual-focused approach include global ratings of change within patients and global ratings of differences between patients. Distribution-based methods rely on expressing an effect in terms of the underlying distribution of results. Investigators may express effects in terms of between-person standard deviation units, within-person standard deviation units, and the standard error of measurement. No single approach to interpretability is perfect. Use of multiple strategies is likely to enhance the interpretability of any particular instrument.

Methods to explain the clinical significance of health status measures.

Background: Dyspnea is a common, distressing symptom of cardiopulmonary and neuromuscular diseases. Since the ATS published a consensus statement on dyspnea in 1999, there has been enormous growth in knowledge about the neurophysiology of dyspnea and increasing interest in dyspnea as a patient-reported outcome.Purpose: The purpose of this document is to update the 1999 ATS Consensus Statement on dyspnea.Methods: An interdisciplinary committee of experts representing ATS assemblies on Nursing, Clinical Problems, Sleep and Respiratory Neurobiology, Pulmonary Rehabilitation, and Behavioral Science determined the overall scope of this update through group consensus. Focused literature reviews in key topic areas were conducted by committee members with relevant expertise. The final content of this statement was agreed upon by all members.Results: Progress has been made in clarifying mechanisms underlying several qualitatively and mechanistically distinct breathing sensations. Brain imaging studies have consist...

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An Official American Thoracic Society Statement: Update on the Mechanisms, Assessment, and Management of Dyspnea

The Paediatric Asthma Quality of Life Questionnaire contains 23 items that children with asthma have identified as troublesome in their daily lives. The aim was to evaluate the measurement properties of the questionnaire. The study design consisted of a 9 week single cohort study with assessments at 1, 5 and 9 weeks. Patients participating in the study were fifty-two children, 7-17 years of age, with a wide range of asthma severity. At each clinic visit, a trained interviewer administered the Paediatric Asthma Quality of Life Questionnaire, the Feeling Thermometer, a clinical asthma control questionnaire and measured spirometry. For 1 week before each clinic visit, patients recorded morning peak flow rates, medication use and symptoms in a diary. The Paediatric Asthma Quality of Life Questionnaire was able to detect quality of life changes in those patients who altered their health status either as a result of treatment or natural fluctuations in their asthma (p < 0.001) and to differentiate these patients from those who remained stable (p < 0.0001). It was reproducible in patients who were stable (ICC = 0.95), which also indicates the instrument's strength to discriminate between subjects of different impairment levels. The questionnaire showed good levels of both longitudinal and cross-sectional correlations with the conventional asthma indices and with general quality of life. The results were consistent across individual domains and different age strata. The Paediatric Asthma Quality of Life Questionnaire has good measurement properties and is valid both as an evaluative and a discriminative instrument. It captures aspects of asthma most important to the patient and adds additional information to conventional clinical outcomes.

Measuring quality of life in children with asthma.

Parents and primary caregivers of children with asthma are limited in normal daily activities and experience anxieties and fears due to the child's illness. We have developed the Paediatric Asthma Caregiver's Quality of Life Questionnaire (PACQLQ) to measure these impairments. The objective of this study was to evaluate the measurement properties of the PACQLQ. A 9-week single cohort study was conducted with assessments at 1, 5 and 9 weeks. Participants in the study were primary caregivers of 52 children (age 7–17 years) with symptomatic asthma, recruited from notices in the local media and paediatric asthma clinics. Caregivers completed the PACQLQ, Impact-on-Family Scale and Global Rating of Change Questionnaires. Patients completed the Paediatric Asthma Quality of Life Questionnaire and an asthma control questionnaire. Spirornetry and β-agonist use were recorded. The PACQLQ was able to detect quality of life changes in those caregivers who changed (p<0.001) and to differentiate these from the caregivers whose quality of life remained stable (p<0.0001). The PACQLQ is reproducible in subjects who are stable (ICC=0.84), and showed acceptable levels of longitudinal and cross-sectional correlations with the child's asthma status and health-related quality of life and with other measures of caregiver health-related quality of life. The PACQLQ functions well as both an evaluative and a discriminative instrument.

M. Townsend

Papers

Measuring quality of life in children with asthma.

Measuring quality of life in the parents of children with asthma