The annual United States Peace Index finds the country overall more peaceful than at anytime in the past 20 years, with Maine finishing first as the "most peaceful" state and Louisiana placing last for the 11th year in a row.

In rankings by metropolitan area, the 2012 survey finds Cambridge-Newton-Framingham in Massachusetts as most peaceful and Detroit-Livionia-Dearborn in Michigan as least peaceful.

READ: The 2012 U.S. Peace Index

The survey, issued annually by the Institute for Economics & Peace, defines peace as "absence of violence."

The five criteria used in the ranking are the number of homicides per 100,000 people; number of violent crimes; incarceration rate; number of police employees; and availability of small arms.

The survey, first issued in 1991, finds that the United States improved in all five categories over 2011, including a 3.2% drop in homicides and a 5.5% dip in violent crimes.

The survey finds, however, that the decrease in officially recorded violence has been partially offset by increases in violence in prison.

The survey, once again, notes a strong correlation between peace and economic opportunity, health, education and social capital.

While the upper and lower rankings have remained relatively stable, Wyoming jumped the most, rising six places over last year and finishing in the top 20 for the first time since 1995.

Arizona, which registered a sharp increase in the homicide rate, had the sharpest fall, dropping nine places over 2011, ending up in the bottom five for the first time.

A sampling of the winners and losers from the survey:

By state

1. Maine 2. Vermont 3. New Hampshire 4. Minnesota; 5. Utah 6. North Dakota 7. Washington 8. Hawaii 9. Rhode Island 10. Iowa.

... 41. Mississippi 42. South Carolina 43. Arkansas 44 Texas 45 Missouri 46 Arizona 47. Florida 48. Nevada 49. Tennessee 50 Louisiana.

By metropolitan area

1. Cambridge-Newton-Framingham, Mass. 2. Edison-New Brunswick, N.J. 3 Seattle-Bellevue-Everett, Wash. 4. Minneapolis-St. Paul-Bloomington, Minn. 5. Peabody, Mass. 6 Providence-New Bedford-Fall River, R.I.-Mass. 7 Lake County-Kenosha County, Ill.-Wis. 8. Nassau-Suffolk, N.Y. 9. Salt Lake City, Utah 10. Portland-Vancouver-Hillsboro, Ore.-Wash.

... 52. Chicago-Naperville-Joliet, Ill. 53. Charlotte-Gastonia-Rock Hill, N.C.-S.C. 54. Los Angeles-Long Beach-Glendale, Calif. 55 Jacksonville, Fla. 56 Las Vegas-Paradise Nev. 57. Houston–Sugar Land–Baytown, Texas 58. Baltimore-Towson, Md. 59. Miami-Miami Beach-Kendal, Fla. 60 New Orleans-Metairie-Kenner, La. 61. Detroit-Livonia-Dearborn, Mich.