18 Since then, migration has increased steadily and at the end of 2017 the percentage of those born abroad was more than 18 per cent. The migration streams can vary substantially from year to year, but the trend has been rising and there has been a particularly substantial increase in recent decades, see Figure 9. Figure 9. Immigration and emigration as a proportion of population, 1900–2018 1.8  1.8 Immigration 1.5  Emigration  1.5  1.2  1.2  0.9  0.9  0.6  0.6  0.3  0.3  0 1900  1915  1930  1945  1960  1975  1990  2005  0  Note. Per cent of the population. To be counted as an emigrant, a person must have the intention of living abroad for at least one year. To be counted as an immigrant, a person must have the intention of staying in Sweden for at least one year. Source: Statistics Sweden  Immigration to Sweden follows an international trend with increasingly large migration streams. Between 2000 and 2017 the total number of migrants in the world increased by around 50 per cent. There are roughly around 260 million migrants at the moment, most of whom are from low-income countries. These migrants move at approximately the same extent to low income countries as to high income countries, see Figure 10a. Migration from high income countries is much less common, but there is a not insignificant amount of migration between high income countries.
In the long run, when inflation is on target and resource utilisation is at its long-term sustainable level, the Taylor rule can be described as follows, 𝑅𝑅𝑡𝑡 = 𝑅𝑅� = 𝒓𝒓∗ + 2,  where 𝑅𝑅� refers to the long-term level of the policy rate and 2 is as before the central bank's inflation target. The long-term policy rate is thus equal to 𝒓𝒓∗ plus the inflation target. If the inflation target is constant, the long-term policy rate, in practice the average policy rate, is determined by 𝒓𝒓∗ . For instance, if 𝒓𝒓∗ declines it means that the policy rate’s long-term (average) level declines at the same pace. We have seen a trend decline in international 𝒓𝒓∗ over a longer period of time, which is an important factor behind the low interest rates in Sweden. I will return to this later. Resource utilisation's long-term sustainable level also plays an important role for monetary policy, but in a slightly different way. The long-term level of the policy rate is namely not affected by 𝒚𝒚∗ , on the other hand, the variations around the long-term level of the policy rate are affected. A simple example can explain why this is the case. Let us assume that resource utilisation is equal to 𝒚𝒚∗ initially and that 𝒚𝒚∗ then rises to a higher level. Resource utilisation is then lower than its long-term level, that is, resource utilisation can be said to be lower than “normal” and we have “an economic downturn”.