We study the correlations between the driving signal reflection on the traveling wave electrodes and the modulated signal characteristics of silicon Mach-Zehnder modulators (MZM). Correlation coefficients are introduced for systematic and quantitative analysis. The signal-to-noise ratio, extinction ratio, and bit error rate show similar correlation behaviors with the mean reflection magnitude over proper frequency ranges, whereas the correlation behaviors of the temporal parameters can be complex. Partial correlation coefficients can be introduced to help remove the influence of other factors. Some relevant fabrication variation scenarios in the underlying structures are discussed, and potential approaches to mitigating the effects of such variations are suggested.