Year Percent 1950 27.25049 1955 28.5628 1960 29.32589 1965 26.02483 1970 22.84342 1975 23.45395 1980 25.69174 1985 29.08911 1990 30.68394 1995 30.51594 2000 30.72933 2005 31.80679 2010 34.06948 2015 35.43537 2020 34.77889 2025 32.61409 2030 30.76515 2035 29.58859 2040 29.51149 2045 29.63891 2050 28.55174 2055 27.00281 2060 25.81294 2065 25.2882 2070 25.09935 2075 24.78585 2080 24.19919 2085 23.52218 2090 23.02558 2095 22.77937 2100 22.67098