After 46 years in power, Fidel Castro, Cuba's president, is known to play only by his own rules. Even so, his recent move to disregard the standard formula for gross domestic product - the world's standard measurement of an economy's growth - has confounded both economists and ordinary Cubans.

The move to declare GDP a capitalist instrument has been brewing for the past year, after José Luis Rodriguez, the economy and planning minister, called GDP a tool designed to measure growth in market economies - and useless as far as Cuba was concerned.