The population attributable risk fraction (PARF) was calculated using the formula below PARF=P(E)(OR−1)1+P(E)(OR−1) where P(E) is the probability of the exposure, in this case the probability of having more risk alleles than those in the lowest decile of the risk score (P(E) =0.9), and the OR refers to the odds of having COPD for individuals in deciles 2 to 10 of the risk score compared to the odds of having COPD for individuals in the lowest decile (decile 1) of the risk score. The ORs were calculated separately in ever and heavy-smokers using a logistic regression adjusted for age, age2, sex, height and the first 10 ancestry principal components, and an additional pack-years adjustment for heavy-smokers, and were then meta-analysed using inverse variance weighting. Confidence intervals were estimated using the formula above with the lower and upper bound of the meta-analysed OR estimated by logistic regression. These analyses were run using UK Biobank data and the COPD case definition described above: individuals with % predicted FEV1<80% and FEV1/FVC<0.7 were selected as COPD cases and those with FEV1/FVC>0.7 and % predicted FEV1>80% were selected as controls.
