It would be more proper to quote the statistic with the following wording:
About half of Americans (up to 57.4%) will meet the criteria for a DSM-IV disorder sometime in their life.
Source: Kessler, R. C., Berglund, P., Demler, O., Jin, R., Merikangas, K. R., & Walters, E. E. (2005, Jun). Lifetime prevalence and age-of-onset distributions of DSM-IV disorders in the National Comorbidity Survey Replication. Arch Gen Psychiatry, 62(6), 593-602.
Note: Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) is a manual published by the American Psychiatric Association (APA) that includes all currently recognized mental health disorders.
City population estimates from:
Table 5. Estimates of Population Change for Metropolitan Statistical Areas and Rankings: July 1, 2008 to July 1, 2009 (CBSA-EST2009-05)
Source: U.S. Census Bureau, Population Division
Release Date: March 2010