Table 5

Interaction between asthma and GRS in relation to FEV1/FVC

ExposurenFEV1/FVC
Intercept*Asthma effect†GRS effect‡GRS×asthma interaction: difference in the effect of GRS per asthma category§Pinteraction
Asthma
 No18030.751−0.003
 Yes10410.704−0.047−0.006−0.0030.053
  • *The intercept at each asthma category is the FEV1/FVC value for a subject in that asthma category calculated at the mean value for all continuous variables in the model (GRS, age, age2, height, height2, pack-years and 10 principal components) and at the reference category for all categorical covariates (ie, never smoker, female and residing at Iowa).

  • †The effect of asthma is obtained by subtracting the intercept value for non-asthmatics from the intercept value for the asthmatics; that is, 0.704–0.751=−0.047 is the difference in FEV1/FVC for an asthmatic relative to a non-asthmatic calculated at the mean value for all continuous variables (GRS, age, age2, height, height2, pack-years and 10 principal components) and at the reference category for all categorical covariates (ie, never smoker, female and residing at Iowa).

  • ‡The effect for the GRS is the individual slope for GRS for each exposure category and is interpretable as the difference in FEV1/FVC per unit increase in the GRS.

  • §The interaction effect between the GRS and asthma is the difference in the effect estimate for the GRS by asthma category and is calculated as the difference in the slope for the GRS for asthmatics relative to non-asthmatics; that is, −0.006−(−0.003)=−0.003.

  • ¶The p value for interaction between the GRS and asthma.

  • GRS, Genetic Risk Score.