Year Percent 1950 29.25364 1955 28.39922 1960 27.17352 1965 26.82527 1970 26.06 1975 26.93636 1980 29.55612 1985 31.42679 1990 33.16648 1995 33.68929 2000 33.00163 2005 32.28855 2010 31.41998 2015 30.96799 2020 30.45703 2025 29.42432 2030 28.23282 2035 27.3294 2040 26.37758 2045 25.52096 2050 24.94128 2055 24.06085 2060 23.31121 2065 22.75529 2070 22.27142 2075 21.84894 2080 21.46997 2085 21.12571 2090 20.82862 2095 20.58536 2100 20.40029