Secular trend in the occurrence of asthma among children and young adults: critical appraisal of repeated cross sectional surveysBMJ 1997; 314 doi: https://doi.org/10.1136/bmj.314.7097.1795 (Published 21 June 1997) Cite this as: BMJ 1997;314:1795
- a Section of Epidemiology, Department of Population Health Sciences, National Institute of Public Health, PO Box 4404, 0403 Oslo, Norway
- b Environmental Epidemiology Unit, Department of Public Health, University of Helsinki, Helsinki, Finland
- Correspondence to: Professor Magnus
- Accepted 15 April 1997
Objectives: To review repeated surveys of the rising prevalence of obstructive lung disease among children and young adults and determine whether systematic biases may explain the observed trends.
Design: Review of published reports of repeated cross sectional surveys of asthma and wheezing among children and young adults. The repeated surveys used the same sampling frame, the same definition of outcome variables, and equivalent data collection methods.
Setting: Repeated surveys conducted anywhere in the world.
Subjects: All repeated surveys whose last set of results were published in 1983 or later.
Main outcome measures: Lifetime and current prevalences of asthma and current prevalence of wheezing. The absolute increase (yearly percentage) in the prevalences of asthma and wheezing was calculated and compared between studies.
Results: 16 repeated surveys fulfilled the inclusion criteria. 12 reported increases in the current prevalence of asthma (from 0.09% to 0.97% a year) and eight reported increases in the current prevalence of wheezing (from 0.14% to 1.24% a year). Changes in labelling are likely to have occurred for the reporting of asthma, and information biases may have occurred for the reporting of wheezing. Only one study reported an increase in an objective measurement.
Conclusions: The evidence for increased prevalences of asthma and wheezing is weak because the measures used are susceptible to systematic errors. Until repeated surveys incorporating more objective data are available no firm conclusions about increases in obstructive lung disease among children and young adults can be drawn.
There is an increase in the reporting of wheezing illness in children
The increase may be due to information bias
There is a lack of objective measurements in population based samples to support claims for an increase in asthma
The changing informational content complicates following the epidemiology of asthma