The world health report 2006 - working together for health, WHO, 2006.

Extract page 11-12 "...countries with fewer than 2.5 health care professionals (counting only doctors, nurses and midwives) per 1000 population failed to achieve an 80% coverage rate for deliveries by skilled birth attendants or for measles immunization...Using a similar “threshold” method and updated information on the size of the health workforce obtained for this report, the JLI analysis has been repeated for skilled birth attendants (see Figure 1.4). A remarkably similar threshold is found at 2.28 health care professionals per 1000 population, ranging from 2.02 to 2.54 allowing for uncertainty. The 57 countries that fall below this threshold and which fail to attain the 80% coverage level are defined as having a critical shortage. Thirty-six of them are in sub-Saharan Africa (Figure 1.5)."

Out-of-pocket health payments and catastrophic expenditures, WHO, 2005.