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Table 4 Univariate linear regression of difference between ITT lower CI and PP lower CI on study characteristics and risk for bias

From: Intention-to-treat analysis may be more conservative than per protocol analysis in antibiotic non-inferiority trials: a systematic review

Predictors Co-efficient (95% CI) P-value
ITT based on assignment alone −0.21 (− 1.60 to 1.18) 0.7654
ITT based on use of drug at least once 0.01 (−1.31 to 1.34) 0.9823
PP exclusion based on concomitant therapy −1.35 (− 2.66 to −0.04) 0.0439
PP exclusion based on incompliance 0.55 (−0.96 to 2.05) 0.4764
PP exclusion based on lost to follow-up 0.41 (−1.04 to 1.87) 0.5757
Proportion of treatment arm in the ITT population that was included in the PP population per every 10% 0.70 (0.09 to 1.32) 0.0247
Proportion of control arm in the ITT population that was included in the PP population per every 10% −0.90 (−1.42 to −3.72) 0.0009
Missing data as failure −0.68 (− 2.05 to 0.68) 0.3263
Tipping point analysis − 2.66 (−7.53 to 2.21) 0.2818
Multiple imputation −1.49 (−5.72 to 2.75) 0.4892
Low risk for allocation concealment bias −0.87 (−2.17 to 0.44) 0.1936
Low risk for performance bias −1.69 (−2.97 to −0.40) 0.0104
Low risk for detection bias −1.21 (−2.54 to 0.11) 0.0728
Low risk for attrition bias −0.56 (−1.93 to 0.82) 0.4264
  1. The dependent variable in the model is ITT lower CI limit minus PP lower CI limit. Therefore, a negative co-efficient is associated with a smaller ITT lower CI limit, so the ITT analysis is more conservative than PP analysis. Conversely, a positive co-efficient is associated with a smaller PP lower CI limit, so the PP analysis is more conservative than the ITT analysis
  2. CI confidence interval, ITT Intention-to-treat, PP Per-protocol