Year Percent 1950 29.57546 1955 26.54773 1960 24.84129 1965 24.90673 1970 24.74143 1975 27.68295 1980 31.03182 1985 32.95709 1990 32.35083 1995 32.04956 2000 31.91413 2005 33.10018 2010 34.02411 2015 33.10356 2020 30.87139 2025 27.85394 2030 26.39051 2035 26.71584 2040 27.3271 2045 26.97984 2050 25.80385 2055 24.62676 2060 24.24401 2065 24.48207 2070 24.81214 2075 24.79134 2080 24.368 2085 23.84668 2090 23.56229 2095 23.56839 2100 23.65924