For example, US real per capita GDP grew by a factor of 1.87 – that is, nearly doubled in size – from 1961 to 1986, but by a factor of only 1.58 from 1978 to 2003. Such differences in 25-year growth rates are important: if US GDP grows by a factor of 1.87 over the next 25 years, annual GDP will be $3.6 trillion ($10,000 per person) higher than if it grows by a factor of only 1.58.