Year	% of total
1971	0.016524754013353116
1972	0.020991164180691916
1973	0.026855131467051225
1974	0.02502442767523622
1975	0.04599368788409644
1976	0.03937843824902579
1977	0.040678587221589665
1978	0.06248816429621257
1979	0.0774756018767425
1980	0.2834953580913133
1981	0.6620806528194259
1982	1.5488299624409552
1983	1.766164423320257
1984	2.2371145579400977
1985	2.982064403505743
1986	2.9519203040473054
1987	3.807535108372382
1988	4.001179114269295
1989	4.043650072722267
1990	3.6335973899584264
1991	3.8396904031200587
1992	4.258884818324347
1993	5.297675452878049
1994	6.6372192292587755
1995	7.353253682099865
1996	7.844832646716111
1997	8.917008408885959
1998	8.93059835140085
1999	9.101215504374887
2000	8.901635338305674
2001	8.783766770485006
2002	8.634259880694769
2003	8.476325829994332
2004	7.784924624201903
2005	7.5212373927303675
2006	7.1553497166691615
2007	6.921459818928806
2008	6.935498807321598
2009	7.608667590194106
2010	7.7170026498645115
2011	6.685271844835194
2012	6.739884162575627
2013	6.550204044113615
2014	6.688712986686436
2015	7.130772890515326