Year Percent 1961 1.96499 1962 1.96499 1963 1.96499 1964 1.96499 1965 1.96499 1966 1.96499 1967 1.96499 1968 1.96499 1969 1.96499 1970 1.96499 1971 1.96499 1972 1.96499 1973 1.96499 1974 1.96499 1975 1.96499 1976 1.96499 1977 2.00071 1978 2.03644 1979 2.1079 1980 2.1079 1981 2.1079 1982 2.21508 1983 2.21508 1984 2.28653 1985 2.28653 1986 2.35798 1987 2.32226 1988 2.39371 1989 2.42944 1990 2.42944 1991 2.46517 1992 2.53662 1993 2.53662 1994 2.57235 1995 2.60807 1996 2.60807 1997 2.60807 1998 2.6438 1999 2.71526 2000 2.71526 2001 2.75098 2002 2.82244 2003 2.96534 2004 3.00107 2005 3.25116 2006 3.39407 2007 3.4298 2008 3.53698 2009 3.64416 2010 3.85852 2011 3.9657 2012 4.03716 2013 4.03716 2014 4.09075 2015 4.14434 2016 4.18006 2017 4.28725 2018 4.28725 2019 4.28725 2020 4.28725 2021 4.28725