A description of what happens to unemployment when the rate of growth of GDP changes, based on empirical research by Arthur Okun (1928–80). It predicts that if GDP grows at around 3% a year, the jobless rate will be unchanged. If it grows faster, the unemployment rate will fall by half of what the growth rate exceeds 3% by; that is, if GDP grows by 5%, unemployment will fall by 1 percentage point. Likewise, a lesser, say 2%, increase in GDP would be associated with a half a percentage point increase in the jobless rate. This relationship is not carved in stone, as it merely reflects the American economy during the period studied by Okun. Even so, in most economies Okun's Law is a reasonable rule of thumb for estimating the likely impact on jobs of changes in output.