The report was prepared by the independent, nonpartisan Transparency International organization, which says it drew its conclusions based "on different assessments and business opinion surveys carried out by independent and reputable institutions."
The information used to compile the index includes "questions relating to the bribery of public officials, kickbacks in public procurement, embezzlement of public funds and questions that probe the strength and effectiveness of public-sector and anti-corruption efforts," Transparency International said.
Perceptions are used, the organization said, because corruption is a hidden activity that is difficult to measure.
"Over time," the organization said in its report, "perceptions have proved to be a reliable estimate of corruption."
The rankings for other Western Hemisphere countries are: Uruguay (25), Puerto Rico (39), Costa Rica (50), Cuba (61), Brazil (73), Colombia, El Salvador and Peru (tied for 80), Panama (86), Argentina and Mexico (tied for 100), Bolivia (118), Ecuador and Guatemala (tied for 120), the Dominican Republic and Honduras (tied for 129), Nicaragua (134), Paraguay (154), Venezuela (172) and Haiti (175).
The index uses a scale of 0-10 to measure perceived corruption, with zero representing highly corrupt and 10 being very clean.
New Zealand, the highest-ranked nation, has a 9.5 score. Somalia and North Korea, the lowest-ranked, have 1.0.
The United States scored 7.1, while Canada is 8.7 and Chile is 7.2. Haiti, the lowest-ranked nation in the Western Hemisphere, scored 1.8. Next-worst is Venezuela with 1.9.
In Eastern Europe and Central Asia, Turkey is ranked highest at 61 with 4.2 on the scale, and Turkmenistan and Uzbekistan are lowest, tied for 177 with a 1.6 index value.
In the European Union and Western Europe, Denmark and Finland are best, tied for second with a 9.4 index value. Bulgaria is lowest at No. 86 with a 3.3 on the corruption scale.
In the Middle East and North Africa, Qatar is best at No. 22 and a 7.2 index value. Iraq is lowest, ranked No. 175 with a 1.8.
In Sub-Saharan Africa, Botswana is ranked highest at No. 32 and a 6.1 index value.
Transparency International, headquartered in Berlin, reports having 90 chapters worldwide. The organization says it works with partners in government, business and civil society to develop and implement effective measures to combat corruption.
The complete report, released Thursday, can be seen at www.transparency.org.