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Table 2 Comparison of the intercept and slope to explain the effect of β2-agonists by IPD

From: Many continuous variables should be analyzed using the relative scale: a case study of β2-agonists for preventing exercise-induced bronchoconstriction

 InterceptSlopeχ2(3 df) *P *AIC **
Uniform effect (absolute scale)27.7  1638.3
Intercept and slope7.9−0.6982.310−17 
Slope (relative scale)−0.9013.90.0031576.8
  1. The intercept and the slope were calculated with a linear mixed-effects model using the type of β2-agonist and study as grouping variables. The intercept alone indicates that β2-agonists decrease the post-exercise FEV1 decline by an absolute effect of 27.7 pp. (95% CI: 22.1 to 33.4 pp). The slope alone indicates that β2-agonists decrease the post-exercise FEV1 decline by a relative effect of 90% (95% CI: 72% to 109%). Abbreviations: pp., percentage points
  2. * Anova test comparing the model on the row with the model on the row above
  3. ** AIC, Akaike information criterion. AIC estimates the relative quality of statistical models, lower AIC value is preferable