Annual % of total
1964 25.901639344262296
1965 32.34880450070323
1966 15.342631898120073
1967 21.107266435986162
1968 19.643882825962088
1969 20.206409560021726
1970 16.756513926325244
1971 16.65268456375839
1972 19.61658493089612
1973 18.885815883050178
1974 20.728744939271255
1975 25.385632437197003
1976 15.215924426450744
1977 18.178233438485805
1978 18.34319526627219
1979 15.948777648428402
1980 17.465753424657535
1981 20.365332296929655
1982 16.47940074906367
1983 17.490361023484056
1984 18.403547671840354
1985 18.113612004287244
1986 14.441340782122905
1987 11.958614051973052
1988 14.301981325438398
1989 13.61576801087449
1990 11.313793103448276
1991 14.968573770491803
1992 16.458814293448835
1993 19.301129976580793
1994 23.16
1995 26.010116279069766
1996 26.8485598923284
1997 31.499609544468544
1998 28.1736105188344
1999 29.878400758533502
2000 24.036248175182482
2001 19.073676258992805
2002 20.28740592473979
2003 22.29737721021611
2004 18.57896622313204
2005 18.91069457659372
2006 19.398168870803662
2007 19.199149590163934
2008 21.18175
2009 21.528838709677416
2010 17.979887869520898
2011 28.404090513489994
2012 30.523005780346818
2013 33.28781553398058
2014 30.694148148148148
2015 29.247282258064516
2016 28.79545950864422