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Table 5 Rate ratios for the multipollutant joint effects of the C&RT-identified mixtures and comparison model

From: Associations between ambient air pollutant mixtures and pediatric asthma emergency department visits in three cities: a classification and regression tree approach

  C&RT-identified mixtures (modeled with indicators) Mixture mean - referent mean Comparison model with continuous terms (linear terms only)
Label RR 95 % CI O3 NO2 PM2.5 RRa 95 % CI
Mixture 1 0.99 (0.97, 1.02) 6.35 1.01 5.04 1.01 (1.00, 1.02)
Mixture 2 1.04 (0.99, 1.09) 7.20 1.18 11.64 1.01 (1.00, 1.03)
Mixture 3 1.01 (0.98, 1.04) −2.89 7.56 5.18 1.01 (1.00, 1.02)
Mixture 4 1.03 (1.01, 1.06) −1.05 12.11 3.83 1.02 (1.00, 1.03)
Mixture 5 1.04 (1.01, 1.07) 4.06 19.34 5.14 1.04 (1.02, 1.06)
Mixture 6 1.03 (0.99, 1.08) 14.37 7.63 4.97 1.03 (1.02, 1.05)
Mixture 7 1.02 (0.99, 1.06) 14.24 11.91 3.12 1.04 (1.02, 1.06)
Mixture 8 1.04 (1.01, 1.08) 23.43 2.68 0.98 1.04 (1.02, 1.06)
Mixture 9 1.00 (0.97, 1.03) 24.15 0.94 5.56 1.04 (1.02, 1.06)
Mixture 10 1.07 (1.03, 1.12) 24.96 3.35 11.74 1.04 (1.02, 1.07)
Mixture 11 1.04 (0.99, 1.08) 23.48 7.53 5.52 1.05 (1.03, 1.07)
Mixture 12 1.04 (0.99, 1.08) 23.84 15.68 0.92 1.06 (1.04, 1.09)
Mixture 13 1.06 (1.02, 1.09) 24.15 16.29 7.46 1.06 (1.04, 1.09)
Mixture 14 1.01 (0.97, 1.05) 35.53 1.98 6.09 1.06 (1.03, 1.09)
Mixture 15 1.03 (0.98, 1.08) 37.21 7.71 6.16 1.07 (1.04, 1.10)
Mixture 16 1.05 (1.01, 1.09) 41.33 12.04 10.94 1.08 (1.05, 1.12)
Mixture 17 1.05 (1.01, 1.09) 42.56 20.37 11.55 1.10 (1.06, 1.14)
Wald Testb χ 2df = 18 c = 36.6, p = 0.006     χ 2df = 3 =27.06, p < 0.001
  1. C&RT classification and regression tree, CI confidence interval, DF degrees of freedom, RR rate ratio
  2. aRate ratios calculated for the effect of an increase equal to the mixture mean minus the referent mean for all pollutants
  3. bSimultaneous Wald test for all exposure parameters in the model
  4. cThere are 18, as opposed to 17, degrees of freedom to account for the Day-Types not included in any mixture