Year	% of total
1971	3.3765587667147337
1972	2.785820783670194
1973	3.133976121458127
1974	3.791288712089714
1975	3.469340143154404
1976	3.3871928176547863
1977	3.818435125917735
1978	4.102325405602907
1979	4.565126615268781
1980	4.711467636120151
1981	5.216057675855375
1982	6.35046412773528
1983	7.484941189014621
1984	8.333469902961966
1985	9.837587516025973
1986	10.307544392224251
1987	13.770533083931605
1988	15.778644781557908
1989	16.77853658643916
1990	17.82038979106578
1991	18.575551651040513
1992	20.15200781778221
1993	20.060386082582674
1994	21.381050223239573
1995	23.136319368209055
1996	23.59015988011351
1997	23.305228745054375
1998	22.278746494507295
1999	22.238389309697894
2000	22.038688204013287
2001	21.49736384295316
2002	21.87313750891357
2003	23.15839060676874
2004	25.935446698222176
2005	25.68699834730755
2006	25.761163078789817
2007	24.84634570933201
2008	26.180517996198176
2009	26.529692548660005
2010	29.09197535464912
2011	27.09384652880419
2012	27.845251931922064
2013	27.90472994522451
2014	28.037488996210563
2015	28.302524055927726