There is no winner this year for the world's most valuable individual prize - the Mo Ibrahim prize for good governance in Africa.
Nigeria, South Africa, Kenya and Egypt dropped in the rankings in two of the four categories used in the index to assess good governance across the continent – safety and rule of law, and participation and human rights. The other two categories are sustainable economic opportunity and human development.
Nigeria was singled out as the worst performer of the four, dropping into the bottom 10 countries in the overall rankings for the first time. The country was ranked 14th out of the 16 countries in west Africa and 43rd out of the 52 countries listed overall. Nigeria was 41st last year and 37th in 2006.
Although South Africa, Egypt and Kenya are ranked fifth, 14th and 25th respectively, people's freedom to participate in political processes has declined in each country. Kenya and South Africa have also registered a decline in economic opportunities, while Egypt has shown a significant improvement in this area.
The $5m (£3.2m) prize is supposed to be awarded each year to a democratically elected leader who governed well, raised living standards and then voluntarily left office.
The panel said no candidate had met all of the criteria - as in 2009 and 2010.
Last year, Cape Verde President Pedro Verona Pires won the prize.
He led the fight against Portuguese colonialism, introduced multi-party politics and was praised for living standards.
The $5m prize is spread over 10 years and is followed by $200,000 a year for life.
"The prize committee reviewed a number of candidates but none met all of the criteria needed to win the prize," said committee member Salim Ahmed Salim.
The two other winners in the six years since the prize was launched were Botswana's President Festus Mogae and Mozambique's Joaquim Chissano.
Earlier this month, Mr Ibrahim's foundation announced a special $1m award to Archbishop Desmond Tutu for "speaking truth to power".
The London-based body called the cleric "one of Africa's great voices for justice, freedom, democracy and responsible, responsive government".
Sudan-born telecoms entrepreneur Mr Ibrahim says the good governance prize is needed because many leaders of sub-Saharan African countries come from poor backgrounds and are tempted to hang on to power for fear that poverty awaits them when they leave office.