Ghana’s statistics agency will release revised economic growth figures for the past four years, following a plan to re-calculate the way gross domestic product is valued in the West African nation.

The data may mean the economy, which will grow by 5.9 percent this year with gross domestic product of $17.95 billion according to an estimate made using the current base, is “40 to 50 percent bigger than previously thought,” said Wayne Mitchell, the International Monetary Fund’s resident representative in phone interview from the capital, Accra, today.

The revised figures will be released before the finance ministry announces its budget for 2011, likely in mid-November, said Bernice Ofosu-Baadu, the Ghana Statistical Service’s head of national accounts and economic indicators.

The reference year has been updated to 2006, from 1993, and industries such as communications and financial services are being separated from other groups, she said in a phone interview yesterday.

The statistical agency will also begin quarterly reporting of economic growth figures, Ofosu-Baadu said.

To contact the reporter on this story: Moses Mozart Dzawu in Accra at mdzawu@bloomberg.net.