In the nineteenth century D.S. fertility declined steadily at approximately 0.8 percent per annum; there was no twenty-year span when the rate of change departed markedly from this long-term trend. During the twentieth century the average rate of decline has been similar, about 0.9 percent per annum, but the rate of change has been extremely unstable (see Figure 2.1). Between 1925 and 1935 fertility plummeted at the rate of 3.2 percent per annum. From 1935 to 1955 fertility actually rose by 2.1 percent per annum; then between 1955 and 1975 it fell at 2.9 percent per annum. Economic factors appear to have been significant in all these cyclical swings.