Year	% 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