Year	% of total
1971	25.55138432660723
1972	24.64741437206179
1973	20.47684234542551
1974	18.554372378186514
1975	15.987173614292258
1976	16.438503826668104
1977	15.988134206219312
1978	16.43822393822394
1979	16.64271600502964
1980	14.739171134371542
1981	13.449657705793955
1982	12.492629096116586
1983	9.909695817490494
1984	7.497962510187449
1985	5.9401709401709395
1986	5.5005425935973955
1987	4.885847668990215
1988	4.469405852793379
1989	7.282016731233508
1990	9.623339865011975
1991	6.753168678923902
1992	4.811519026964182
1993	5.266008415614714
1994	5.981722514538909
1995	3.7142755200342528
1996	7.639996095402337
1997	6.697300057062197
1998	5.500014080937228
1999	8.848658504818964
2000	4.254204301611857
2001	2.9978133596670666
2002	3.388976666437682
2003	4.029554335988383
2004	5.536244336822371
2005	6.462922033381602
2006	4.909616775126537
2007	25.269616640175013
2008	26.949618116039126
2009	20.007575508053094
2010	14.015289406625408
2011	9.670841386027117
2012	8.808475864145317
2013	7.460480394169575
2014	6.578542883492161
2015	4.186398185363524