Table:
text: Demographics of Kazakhstan
Population of Kazakhstan 1939-2009
Population of Kazakhstan 1939-2009
Year_January Population_000 Rural_ Urban_ Source_
1939 6081 72 28 census
1959 9295 56 44 census
1970 13001 50 50 census
1979 14685 46 54 census
1989 16537 43 57 census
1999 14953 43 57 census
2002 14851 43 57 estimate
2005 15075 43 57 estimate
2008 15572 47 53 estimate

Question: What were the demographic factors of Kazakhstan, for how many years the urban population was 57% for 1939-2009?