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Related Experiment Videos

Measuring changes in logarithmic data, with special reference to bronchial responsiveness

J K Peat1, W R Unger, D Combe

  • 1Department of Medicine, University of Sydney, NSW, Australia.

Journal of Clinical Epidemiology
|October 1, 1994
PubMed
Summary
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Bronchial hyperresponsiveness measurements in asthma studies are log-normally distributed. Report changes using log-based units like doubling dose or percent change for accurate longitudinal analysis.

Area of Science:

  • Respiratory Medicine
  • Clinical Trials
  • Biostatistics

Background:

  • Bronchial provocation tests (e.g., histamine, methacholine) assess airway hyperresponsiveness, a hallmark of asthma.
  • Measurements of bronchial responsiveness follow a log-normal distribution, complicating longitudinal data analysis.

Purpose of the Study:

  • To provide statistically correct methods for reporting within-subject changes in bronchial responsiveness measurements.
  • To guide the use of appropriate logarithmic units for longitudinal studies and clinical trials.

Main Methods:

  • Explains statistical methods for calculating changes in bronchial responsiveness.
  • Focuses on log-based units: doubling dose, fold difference, and percent change.
  • Applicable to repeatability and agreement calculations for log-normally distributed data.

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Main Results:

  • Standard units (e.g., dose) are inappropriate for longitudinal changes in log-normally distributed data.
  • Log-based units (doubling dose, fold difference, percent change) are statistically correct for within-subject changes.
  • 'Doubling dose' is specific to concentration doubling protocols; 'fold difference' and 'percent change' are broadly applicable.

Conclusions:

  • Accurate reporting of longitudinal changes in bronchial responsiveness requires log-based units.
  • The described methods ensure statistical validity in clinical trials and epidemiological studies of respiratory illnesses.
  • These statistical approaches are also relevant for assessing test method repeatability and agreement.