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

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 ...

/pdf/an-official-american-thoracic-society-european-respiratory-18b801porh.pdf

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 For children younger than 12 years old with asthma, there are several quality-of-life instruments, clinical diaries, and questionnaires assessing symptoms; however, a validated tool for assessing asthma control is currently lacking. Objective To develop and validate the Childhood Asthma Control Test (C-ACT), a self-administered tool for identifying children aged 4-11 years whose asthma is inadequately controlled. Methods A 21-item questionnaire was administered to 343 patients with asthma and their caregivers, randomly assigning 75% (n = 257) for development and cross-sectional validation of the tool and 25% (n = 86) to a confirmatory sample. Stepwise logistic regression was used to reduce the 21 items to those best able to discriminate control as defined by the specialist's rating of asthma control. Results Seven items were selected from regression analyses of the development sample to comprise the C-ACT. The scores of each item were summed for a total score (0-27), with lower scores indicating poorer control. Summed scores discriminated between groups of patients differing in the specialists' rating of asthma control (F = 36.89; P Conclusion The C-ACT is a validated tool to assess asthma control and identify children with inadequately controlled asthma. Clinical implications The C-ACT can be valuable in clinical practice and research based on its validation, ease of use, input from the child and caregiver, and alignment with asthma guidelines.

Development and cross-sectional validation of the Childhood Asthma Control Test

Over the past decade, the methods and science used to describe changes in outcomes of physical therapy services have become more refined. Recently, emphasis has been placed not only on changes beyond expected measurement error, but also on the identification of changes that make a real difference in the lives of patients and families. This article will highlight a case example of how to determine and interpret "clinically significant change" from both of these perspectives. The authors also examine how to use item maps within an item response theory model to enhance the interpretation of change at a content level. Recommendations are provided for physical therapists who are interpreting changes in the context of clinical practice, case reports, and intervention research. These recommendations include a greater application of indexes that help interpret the meaning of clinically significant change to multiple clinical, research, consumer, and payer communities.

/pdf/interpreting-change-scores-of-tests-and-measures-used-in-3hkxa1ferk.pdf

Interpreting Change Scores of Tests and Measures Used in Physical Therapy

In this study, the perceptions of asthmatics to change in their disease was associated with observed changes in clinical asthma measures, in order to identify the threshold where changes in clinical asthma measures are perceivable by patients. The study included 281 asthmatic patients, aged 18-63 yrs, in a randomized, placebo-controlled clinical trial of a leukotriene antagonist. Changes were related in: 1) asthma symptom scores; 2) inhaled beta-agonist use; 3) forced expiratory volume in one second (FEV1); and 4) peak expiratory flow (PEF) to a global question that queried overall change in asthma since starting the study drug. Additional analyses examined differences in the group reporting minimal improvement by treatment (active treatment versus placebo), sex and age groups. The average minimal patient perceivable improvement for each measure was: 1) -0.31 points for the symptom score on a scale of 0-6; 2) -0.81 puffs x day(-1) for inhaled beta-agonist use; 3) 0.23 L for FEV1; and 4) 18.79 L x min(-1) for PEF. In general placebo-treated patients and older patients, who reported minimal improvement, experienced less mean improvement from baseline than active-treated patients and younger patients, who reported minimal improvement. Determining the minimal patient perceivable improvement value for a measure may be helpful to interpret changes. However, interpretation should be carried out cautiously when reporting a single value as a clinically important change.

https://erj.ersjournals.com/content/erj/14/1/23.full.pdf

What are minimal important changes for asthma measures in a clinical trial

The measurement characteristics of two asthma symptom diary scales developed for use as health outcome measures in clinical trials of asthma therapy were investigated. A daytime diary scale was designed to capture the frequency and inconvenience of daytime asthma symptoms and their effects on activities, and a nocturnal asthma symptom diary scale was designed to capture awakenings with asthma symptoms. The internal consistency, reliability, validity and responsiveness of both asthma diary scales were assessed in 346 adult asthma patients in two placebo-controlled clinical trials of an investigational asthma therapy, a leukotriene biosynthesis inhibitor. The daytime symptom scale showed sufficient internal consistency (0.90-0.92), and the daytime and nocturnal symptom scales showed sufficient test retest reliability (0.69-0.87). Construct validity was demonstrated by generally moderate-to-strong correlations for changes in the diary scales with changes in other measures of asthma status, such as forced expiratory volume in one second (FEV1), peak expiratory flow (PEF), and puffs of beta-agonist inhaler. Both scales demonstrated significant responsiveness to change in asthma due to therapy in one of the clinical trials. Based on these results, the daytime and nocturnal asthma symptom diary scales show measurement characteristics appropriate for use as asthma outcome measures in clinical trials of asthma therapy.

https://erj.ersjournals.com/content/erj/10/3/646.full.pdf

B.l Barber

Papers

What are minimal important changes for asthma measures in a clinical trial

Measurement characteristics of two asthma symptom diary scales for use in clinical trials