The map above ranks countries based on the percentage of people who reported having paid a bribe in one of eight different government services in the past year, including in sectors like medical care, police, judiciary, and land registration. Sierra Leone, Liberia, and Yemen had the highest percentages, with about three-quarters or more of the population saying they had bribed someone. Worldwide, one in four people report having paid a bribe, and police were the most commonly bribed institution.

It's a great guide to the countries that still have far to go in combatting buyoffs, but, frustratingly, data for a few notorious countries are missing: Russia, China, and Brazil among them.

In countries where bribes have become endemic, they can act as a type of regressive tax on the poor and can prevent low-income households from accessing basic services, as the report notes:

The East Africa Bribery Index for example finds that the average bribe paid for land services is more than$100 (9,842 Kenyan Shilling) in Kenya and the average value of a bribe paid to the judiciary in Uganda is more than $200 (594,137 Ugandan Shilling). A survey in Mexico finds that the cost of bribery has a regressive effect on Mexican households hurting the poor the most, with an average-income household spending 14 percent of that income on bribes and those with the lowest incomes spending 33 percent. In Greece, the total costs households incurred due to corruption were estimated to amount to €420 million in 2012.

Overall, the group found that worldwide corruption has increased, with political parties perceived as "the most corrupt public institution."

The group recommends as one of its solutions that "people should refuse to pay a bribe, wherever asked and whenever possible," but that's probably a tall order in countries where getting medical treatment or police help depends on greasing palms.