Determine the national and international incidence of a chosen illness.
According to the National Institute of Mental Health, the current incidence rate for Bipolar Disorder in the United States is 2.6% of the adult population. Studies for children and adolescents are a little more variable because diagnosis is a little more complicated with this population. There is a lot of debate on how to diagnose childhood onset bipolar disorder so the incidence rate in American children is said to be between 0-3%.
Again, according to NIMH "The severity and impact of bipolar disorder and bipolar-like symptoms are similar across international boundaries, according to a study partially funded by NIMH. The results were published in the March 2011 issue of the Archives of General Psychiatry."
This is directly off the NIMH site and should really help and give you all the information you need:
"Although several studies report prevalence rates of mental disorders on an international level, the numbers have varied because each study tends to use different methodology and definitions. To remedy this, the World Health Organization's World Mental Health (WMH) survey initiative used consistent data collection methods in 11 ...
This sites the NIMH findings regarding the national and international incidence rates of bipolar disorder.