For these variables, missing values were assumed to be missing at random and were imputed using multiple imputation.
25 Zip code data were missing in 4.3% of the sample and were imputed with single imputation.
For continuous variables (cholesterol and plasma vitamin C), missing values were assumed to be missing at random and were imputed using multiple imputation (n=5) with univariate regression models.
Party registration data is available for 32 states, and is imputed in the remaining states (i.e., in Alabama, Georgia, Illinois, Indiana, Michigan, Minnesota, Mississippi, Missouri, Montana, North Dakota, South Carolina, Tennessee, Texas, Vermont, Virginia, Washington, and Wisconsin).
The wage measure includes tips, bonuses, and commissions and is imputed using earnings and information on hours, months, or weeks worked.
Five values were above the value corresponding to the highest standard used and were imputed by 1.5 times this specific value.
Patients on adalimumab or etanercept were compared, and were imputed together due to having identical characteristics.
The presence/absence of these pairs was treated as hidden variables and were imputed by the reconstruction algorithm.
Missing values occurred for only 0.7% of all confounders and were imputed once using R software [ 14, 15].
