Year Percent 1950 28.35888 1955 27.71414 1960 27.08005 1965 26.35526 1970 26.26252 1975 26.17637 1980 26.21769 1985 26.79004 1990 27.65653 1995 27.24593 2000 27.85425 2005 29.01558 2010 31.4099 2015 34.03728 2020 35.05943 2025 34.57494 2030 33.61332 2035 32.93267 2040 32.81787 2045 32.72592 2050 32.08887 2055 31.10524 2060 30.03382 2065 29.13191 2070 28.36418 2075 27.59625 2080 26.76204 2085 25.91869 2090 25.15699 2095 24.52342 2100 24.00827