Year Percent 1950 29.49915 1955 29.12278 1960 28.26987 1965 27.57126 1970 26.96065 1975 26.45868 1980 24.28767 1985 23.98977 1990 27.68489 1995 29.81678 2000 31.50772 2005 30.86331 2010 30.95114 2015 32.38347 2020 33.17401 2025 33.23499 2030 32.73075 2035 32.5028 2040 32.42893 2045 32.49534 2050 32.31705 2055 31.4753 2060 30.65995 2065 30.00283 2070 29.48179 2075 28.96952 2080 28.37201 2085 27.68046 2090 26.96539 2095 26.31895 2100 25.77556