Annual % of total
1960 20.569172316173727
1961 19.23134664464795
1962 16.917910980924482
1963 15.907284768211921
1964 14.49635922330097
1965 12.57099361789332
1966 10.43140028288543
1967 10.936918743689217
1968 8.524899693179137
1969 7.489397794741305
1970 7.569863448713877
1971 7.473556441824172
1972 6.4013840830449835
1973 6.648478488982162
1974 7.2431836959515286
1975 8.774556508325395
1976 7.453699858815713
1977 6.269498696525493
1978 7.1326478860251745
1979 8.104490500863557
1980 8.937605396290051
1981 7.87472272103095
1982 10.814151998587155
1983 13.473392879607498
1984 17.00031979533099
1985 18.836320893329418
1986 18.985695708712615
1987 18.747313478661347
1988 19.2658793488669
1989 19.453248811410457
1990 20.647925023430176
1991 18.97726585545723
1992 17.194514537444935
1993 18.40962484516015
1994 19.30989912805608
1995 18.841944015112485
1996 18.153522388059702
1997 17.363609271523178
1998 16.61962816997944
1999 16.135568360398114
2000 17.44715653153153
2001 20.05325142857143
2002 20.106727138097003
2003 18.41471739130435
2004 21.034442993095727
2005 19.718980282812186
2006 20.772167689161556
2007 21.42324565125159
2008 20.102946912242686
2009 17.1890625
2010 19.778790774984415
2011 21.29146221125813
2012 19.70523131672598
2013 20.781173859432798
2014 20.47330179028133
2015 20.52397448979592
2016 20.249327146171694