1966 3.99
1967 3.77
1968 3.42
1969 4.07
1970 4.34
1971 3.89
1972 3.69
1973 4.21
1974 4.12
1975 4.21
1976 3.99
1977 4.47
1978 4.10
1979 4.46
1980 4.29
1981 4.00
1982 4.30
1983 4.31
1984 4.26
1985 4.33
1986 4.41
1987 4.72
1988 4.14
1989 4.13
1990 4.26
1991 4.31
1992 4.12
1993 4.60
1994 4.92
1995 4.85
1996 5.04
1997 4.77
1998 4.79
1999 5.08
2000 5.14
2001 4.78
2002 4.62
2003 4.73
2004 4.81
2005 4.59
2006 4.86
2007 4.80
2008 4.65
2009 4.61
2010 4.38
2011 4.28
2012 4.32
2013 4.17
2014 4.07
2015 4.25
2016 4.48
2017 4.65
2018 4.45
2019 4.85