Changes of HbA1c from baseline to the end in different parts. The black bar indicates the HbA1c of saxagliptin-added group, the white bar indicates that of vildagliptin-added group and the gray bar indicates that of sitagliptin-added group. Bars represent the differences of the mean HbA1c from baseline to the end. Picture A shows the changes in three age stages (<50 years, 50-64years, and >65 years). Picture B shows the changes in three duration stages (<1 year, 1-5years, and >5 years). Picture C shows the changes in three different background therapeutic regimens (metformin with glimepiride, metformin with acarbose, metformin with pioglitazone). Repeated measured ANOVA test and polynomial were used for statistical analysis.