Data analysis
RA
REGRESSION, SECONDARY, DISEASE CHARACTERISTIC
Data analysis was conducted on the modified intent-to-treat (mITT) population including all patients receiving at least one dose of SC abatacept. Descriptive statistics including the mean and standard deviation (SD) for continuous variables and frequency distributions for categorical variables were produced for all patient demographic data and baseline disease characteristics. The proportion of patients achieving the primary endpoint (sustained CDAI LDA) was compared between groups with a cluster-correct (Rao-Scott) Chi-square test; non-responder imputation was used for missing data. Time to achieve the primary endpoint was assessed with a Cox proportional hazard model with shared-frailty to account for the cluster effect and adjusted for site (random effect), site size (number of patients enrolled at each site), and potential confounders identified from the baseline comparison of the treatment groups (prior bDMARD use, smoking status). Achievement of secondary endpoints was assessed with mixed effects logistic regression for repeated measures adjusted for the same covariates as for the primary endpoint. Time to achieve secondary endpoints was assessed with the Kaplan–Meier (K-M) estimator of the survival function and compared between groups with the log-rank test. Least squares mean (LSM) changes from baseline in CDAI, SDAI, DAS28-CRP, RAPID3, and HAQ-DI were estimated with mixed models for repeated measures (MMRM) adjusting for the same covariates as for the primary endpoint. In MMRM, missing data are predicted by the observed data via the model for the conditional mean. The mean (95% confidence interval [CI]) count of changes per patient in RA treatment (NSAIDS, non-biologic/biologic DMARDs, intra-articular steroids, SC abatacept dose), including treatment interval modifications, were compared between groups using a cluster-corrected Student’s t-test. Given the observational nature of the study, no adjustment for multiplicity took place. All statistical analyses were performed using SAS software (