Between 1947 and 1974, the Swedish economy grew at an average rate of 12.5% annually[citation needed]. The urban population, living in towns of over 15,000 people, grew from 38% of the total population in 1931 to 74% by 1973. Sustained by an export boom of automobiles, heavy machinery, electronics, ship-building, and heavy weapons, the per capita income increased by as much as 2000%.