Different definitions in childhood asthma: how dependable is the dependent variable?

Abstract

There is abundant literature on how to select and statistically deal with predictors in prediction models. Less attention has been paid to the choice of the outcome. We assessed the impact of different asthma definitions on prevalence estimates and on the prediction model's performances.We searched PubMed and extracted data of definitions used to diagnose childhood asthma (between 6 and 18 yrs) in cohort studies. Next, using data from an ongoing cohort study (n5186), we constructed and compared four prediction models which all predict asthma at age 6 yrs, using a fixed set of predictors and four different definitions in turn. We defined an area of clinical indecision (posterior probability between 25% and 60%) and calculated the number of children who remained inside this area.122 papers yielded 60 different definitions. Prevalence estimates varied between 15.1% and 51.1% depending on the asthma definition used. The percentage of children whose posterior asthma probability was in the area of clinical indecision varied from 14.9% to 65.3%.Variation in definitions and its effect on the performance of prediction models may be another source of otherwise inexplicable variation in daily clinical decision making. More uniformity of operational asthma definitions seems needed.

Characterizing wheeze phenotypes to identify endotypes of childhood asthma, and the implications for future management

“…One of the challenges to understanding the pathophysiology and aetiology of this disease is the lack of consensus in defining asthma in the medical literature. A recent systematic review showed that in 122 publications investigating risk factors associated with childhood asthma, 60 different definitions were used [2]. Although many of these definitions were similar (with apparently subtle differences between them), the impact of this heterogeneity on the reported results and our understanding of asthma is unclear.…”

“…Although many of these definitions were similar (with apparently subtle differences between them), the impact of this heterogeneity on the reported results and our understanding of asthma is unclear. When four of the most commonly used definitions were applied to a high risk population of 186 children, the overall agreement was 61%, indicating that 39% of the children could move from 'asthma' to 'not asthma' depending on which definition was used [2]. Such variability will obviously affect the performance of prediction models.…”

Reduced neonatal lung function and wheezing illnesses during the first 5 years of life

“…Fourthly, in studies about asthma in children, several definitions of asthma and wheezing phenotypes are used [23]. To accomplish a large sample of newborns and a high participation rate, it was decided not to perform invasive tests in the WHISTLER project.…”

Preterm Birth with Childhood Asthma: The Role of Degree of Prematurity and Asthma Definitions

“…Of the 30 major studies on the association published worldwide, nearly a third reported null effects, whereas the others reported significant associations, with odds ratios ranging from 1.2 to 4.9 (4). We suspected that inconsistencies in the PTB-asthma association in part reflected differences among studies in three key domains: definitions of asthma (6), degree of prematurity, and the age when asthma was assessed.…”