Year Percent 1950 28.30669 1955 28.17238 1960 28.56622 1965 27.73076 1970 25.81886 1975 24.83533 1980 24.78104 1985 26.82836 1990 28.83207 1995 31.54772 2000 35.2011 2005 38.60104 2010 39.14666 2015 35.95112 2020 33.03383 2025 30.90717 2030 29.74962 2035 29.73708 2040 29.53959 2045 28.79254 2050 27.38436 2055 25.64535 2060 24.5638 2065 24.12453 2070 24.07556 2075 24.01774 2080 23.6744 2085 23.09011 2090 22.52202 2095 22.19695 2100 22.13675