3[3]Ayah Johnson, Julie Sochalski, Marshall Fritz, et al. The Registered Nurse Population:Findings from the National Sample Survey of Registered Nurses[EB/OL].http://bhpr.hrsa.gov/healthworkforce.
4[4]World Health Organization .WHO Estimates of Health Personnel[EB/OL].http://www.who.int/whosis/health_personnel/health_personnel.cfm.