Year Percent 1950 31.09699 1955 30.19799 1960 29.15125 1965 27.97375 1970 27.22943 1975 28.12367 1980 29.04978 1985 29.98215 1990 30.73174 1995 30.80512 2000 31.00664 2005 31.56933 2010 32.1754 2015 32.71893 2020 33.0328 2025 32.90722 2030 32.46368 2035 31.50703 2040 30.53875 2045 29.52888 2050 28.58752 2055 27.9497 2060 27.16006 2065 26.33018 2070 25.57596 2075 24.98186 2080 24.55416 2085 24.21094 2090 23.85891 2095 23.50173 2100 23.17222