title: A half doubling dose change in bronchial hyperresponsiveness in a population represents an important difference.
abstract: BACKGROUND
  The prevalence of asthma has increased over recent decades and the reasons for this are poorly understood. A sensitive tool that can evaluate potential risk factors for asthma is bronchial hyperresponsiveness (BHR), a key physiological characteristic of asthma. However, although the minimum clinically important difference in BHR for an individual is accepted to be around one doubling dose, the minimum important change in a population is not defined. As with surrogate measures of cardiovascular disease risk such as blood pressure and cholesterol, a change that is not clinically important in an individual may be extremely important in public health terms.
  
  
  RESULTS
  To assess the potential impact of a small absolute change in BHR across a population, we modelled the effect of different changes in BHR on the prevalence rates of moderate and severe BHR in an asthmatic population. We calculate that a one half doubling dose increase in BHR increases the prevalence of moderate and severe BHR by 30%. If this was accompanied by an equivalent increase in the population prevalence of moderate and severe asthma, this would be highly significant in public health terms.
  
  
  CONCLUSIONS
  We propose that a one half doubling dose worsening in BHR across a population may represent an important change.
authors.affiliation: University of Otago Wellington, Wellington, New Zealand.
authors.forename: Mark
authors.initials: M
authors.lastname: Weatherall
authors.affiliation: Medical Research Institute of New Zealand, Private Bag 7902, Newtown, Wellington, 6242, New Zealand.
authors.forename: James
authors.initials: J
authors.lastname: Fingleton
authors.affiliation: University of Otago Wellington, Wellington, New Zealand.|Medical Research Institute of New Zealand, Private Bag 7902, Newtown, Wellington, 6242, New Zealand.
authors.forename: Sally
authors.initials: S
authors.lastname: Eyers
authors.affiliation: Medical Research Institute of New Zealand, Private Bag 7902, Newtown, Wellington, 6242, New Zealand. Richard.Beasley@mrinz.ac.nz.
authors.forename: Richard
authors.initials: R
authors.lastname: Beasley
keywords: Asthma; Bronchial hyperreactivity; Bronchial hyperresponsiveness; Medication use; Outcome assessment (Health care)