Year	% of total
1960	5.8326167956434505
1961	6.920232435287903
1962	10.02466091245376
1963	11.700382722799343
1964	12.853392568659128
1965	12.488419492310543
1966	11.775409409929816
1967	9.615873823454592
1968	10.451977401129943
1969	10.059126743480897
1970	9.103911893012945
1971	8.114743506913037
1972	7.136773973769375
1973	6.7076790243375966
1974	8.402379434884216
1975	7.804901770083641
1976	7.331282624906786
1977	6.861802024643855
1978	6.875449964002881
1979	6.340005434290371
1980	6.6250663834306955
1981	6.17278691318054
1982	6.003203844613536
1983	5.78643415241762
1984	5.87849411421699
1985	5.515077189438753
1986	5.473124300111982
1987	5.504618660073486
1988	5.543660086985614
1989	7.443076726832068
1990	8.154346815434682
1991	8.436448822681403
1992	8.46962971970572
1993	8.487235594456601
1994	7.925167140110758
1995	7.506516554822252
1996	7.28484084117018
1997	7.424075022231803
1998	8.335105817292353
1999	8.924557738583177
2000	9.246566616556679
2001	8.771353482260185
2002	8.26503236604396
2003	8.07072614464036
2004	8.44777653213752
2005	9.951591882331037
2006	10.419246823540204
2007	11.548922359609627
2008	13.29274132859
2009	15.97818332451154
2010	18.09192944949225
2011	19.57601780455455
2012	20.129224652087473
2013	21.006286401035407
2014	23.307665785541893
2015	24.578667571541683