JOHANNESBURG: Africa's small island states are the best governed on the continent, according to an annual study released on Thursday by Harvard researchers, who said economic powerhouse South Africa has slipped in its rankings.

Mauritius, Seychelles and Cape Verde were Africa's best-governed countries, according to Harvard University's Kennedy School of Government. Chad, Sudan and Somalia came in at the bottom of the list, which has been published since 2007.

The index included North African countries for the first time, with Tunisia and Algeria landing in the top 10, boosted by their relative wealth.

"Tunisia, for instance, has an appalling human rights record, but rates so well in terms of human development, economic opportunity, and security that those scores compensate for appropriately low results in the regard for human rights area," the study said.

"South Africa has slipped a little, from fifth to ninth, largely because of its lower scores in the areas of respect for civil and political rights and the rule of law," it said.

The report used data from 2007, the most complete figures available, meaning this year's study leaves out recent turmoil in Mauritania and Guinea as well as Zimbabwe's economic meltdown and election violence.

Zimbabwe ranked 45 out of the 53 nations surveyed. Top oil producers Angola and Nigeria landed at 46 and 38.

The first two editions of the study were financed by the Mo Ibrahim Foundation, created by a wealthy Sudanese-born British telecom magnate with the aim of fostering good governance on the continent and attracting more investment.

The foundation still grants an award for African leadership aimed at encouraging good governance at the highest level. The prize money is around three times that granted by the Nobel jury.