Figure 3

Correlation of annual epidural and cesarean numbers with annual delivery numbers (A, C) and with OAAI (B, D). Data for 2005 (A, B) and 2007 (C, D). The OAAI correlated more closely with both the number of cesarean deliveries and the number of epidurals. Although coupling exists as the OAAI is derived from both cesarean delivery and epidural rates, it is precisely for this reason that a single denominator is a more useful measure of obstetric anesthesia activity than annual delivery numbers.