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. Author manuscript; available in PMC: 2015 Jul 1.
Published in final edited form as: Environ Res. 2014 May 8;0:182–189. doi: 10.1016/j.envres.2014.03.005

Table 3.

Testing interaction: Analysis of Covariance (ANCOVA) with single factor and single covariate.

MODEL 1 (Dependent Variable: Leq10min)
Predictor DF Sum Sq Mean Sq F-value Pr(>F)1
TotalTraffic_log 1 1324.6 1342.6 155.103 <2e-16
City 2 15.5 7.7 0.893 0.414
TotalTraffic_log:City 2 38.9 19.4 2.244 0.114
Residuals 66 571.3 8.7
MODEL 2 (Dependent Variable: Leq10min)
Predictor DF Sum Sq Mean Sq F-value Pr(>F)1
TotalTraffic_log 1 1324.6 1342.6 149.6 <2e-16
City 2 15.5 7.7 0.861 0.427
Residuals 68 571.3 8.7
MODEL 3 ANCOVA (MODEL1, MODEL2)
Res.DF RSS Df Df Sum of Sq F Pr(>F)1
66 571.32
68 610.2 −2 −38.85 2.244 0.11