(adds details on gains, losses)

LONDON, Sept 25 (Reuters) - Mauritius is the best run country in Africa and Somalia is the worst, according to a new good governance index published on Tuesday.

The first annual Ibrahim Index of African Governance rated the performance of 48 nations against a series of criteria including security, human rights, economic stability, just laws, free elections, corruption, infrastructure, poverty and health.

Mauritius scored highest overall on the index, followed by Seychelles, Botswana, Cape Verde and South Africa.

But in individual categories some other countries stood out. Gabon was first on safety and security; Botswana on transparency; and Seychelles on sustainable economic opportunity and also on human development.

At the foot of the table and just ahead of Somalia were the Democratic Republic of Congo, Chad, Sudan and Guinea-Bissau.

Somalia was seen as most lacking rule of law, worst on human rights, and least able to sustain economic opportunity; Sudan was seen as most dangerous; and Chad was lowest on the human development index.

The countries that made the greatest overall gains, based on a study of their performance from 2000-2005, were Rwanda and Ethiopia. The countries that dropped the most in rankings were Guinea-Bissau and Democratic Republic of Congo.

Zimbabwe, in the news because of a political crisis that has lead to a police crackdown and an economic meltdown that has resulted in the world's highest rate of inflation at around 6,600 percent, is 31st on the list.

The index was prepared and complied for the foundation by the Kennedy School of Government at Harvard University.

"We are shining a light on governance in Africa, and in so doing we are making a unique contribution to improving the quality of governance," said Ibrahim Foundation founder and leading Sudanese businessman Mo Ibrahim.

"The Ibrahim Index is a tool to hold governments to account and frame the debate about how we are governed. Africans are setting benchmarks not only for their own continent, but for the world," Ibrahim added.

The Ibrahim Foundation began operating in October 2006 to promote African development with a special focus on sub-Saharan Africa.

Intended to be an annual benchmarking exercise, its index covers a total of 58 criteria grouped under five main headings. Each of these categories generates an overall country score from which the final national index is produced.

"Mo Ibrahim has a vision to promote and recognise good governance that will drive Africa's political and economic renaissance," said former South African President Nelson Mandela.

"This is an African initiative celebrating the successes of new African leadership. It sets an example that the rest of the world can emulate. We call for leaders across the world -- in government, civil society and business -- to endorse its aims and vision."

The full index can be found at www.moibrahimfoundation.org.

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