Year years 1960 66.57016776222942 1961 66.9592447748992 1962 66.87021838000247 1963 66.98324562080218 1964 67.4726981196551 1965 67.53731715057862 1966 67.75271939692372 1967 67.89512025347926 1968 67.78262049755668 1969 67.62541457932043 1970 68.03769923015858 1971 68.14090511256697 1972 68.46411839811331 1973 68.56230436220966 1974 68.8485834373978 1975 68.87207909748507 1976 69.17242302442868 1977 69.56145694759162 1978 69.69214538469753 1979 70.01251607972256 1980 70.14856660402364 1981 70.4280662673549 1982 70.77869623528682 1983 70.85328060983962 1984 71.22262810438664 1985 71.38399759408028 1986 71.71140798121475 1987 71.9959442317097 1988 72.17307268254956 1989 72.33144350212163 1990 72.39895201167558 1991 72.50580102772174 1992 72.82788773242193 1993 72.98017939323084 1994 73.29211484753999 1995 73.4634340571937 1996 73.78164684294691 1997 74.20886591238104 1998 74.46695945372441 1999 74.72508006774893 2000 75.01058054259664 2001 75.4016901960049 2002 75.54717213498893 2003 75.66069372290019 2004 76.21934310596421 2005 76.39524987123487 2006 76.82673219896715 2007 77.11041391070324 2008 77.39404427004055 2009 77.61608443997441 2010 77.88270185492324 2011 78.35600721558366 2012 78.43471065625961 2013 78.7661996250649 2014 79.21439997478984 2015 78.93530335201895 2016 79.30851946924341 2017 79.38156820789267 2018 79.49826707182481 2019 79.80002368383745 2020 78.9616299402231 2021 79.0283508526873 2022 79.25775187578864