- Data assembled as normalized serum levels of complement factors Ba, C3d and fD levels will be initially evaluated with univariate statistics to assure that the quality of the data is adequate for further analyses. The association between each measured parameter (i.e., serum levels of complement factors), AMD diagnosis, and smoking will be assessed in a stratified bivariate fashion using Student t tests or Wilcoxon rank sum tests, as appropriate, and standard measure assessments will be used to check for normality, skewing, etc.