MMP9 and chronic obstructive pulmonary disease: After quantification using Egger's test, the data showed no publication biases between MMP9 (-1562) C/T and susceptibility to COPD in the three genetic models except for the allele model (CC vs. CT+TT, P=0.325; TT vs. CC+CT, P=0.541; CT vs. CC&TT, P=0.553; C allele vs. T allele, P=0.017) (Figure 8).