Year	% of total
1971	0.1444676267781805
1972	0.27584101543127487
1973	0.3090925312516034
1974	0.14440362142641194
1975	0.4649970441622798
1976	0.613344979099259
1977	0.7793514725585868
1978	1.0055624998085804
1979	1.473051181711091
1980	2.0073397854241004
1981	2.380813506798508
1982	2.43899266532593
1983	3.025579184438199
1984	2.4646877842239663
1985	2.5178549588729076
1986	2.1684382838971854
1987	2.561773046572062
1988	2.3161678349420187
1989	2.6988052935260396
1990	2.9658465891221417
1991	2.6700110012758222
1992	2.7004722647905273
1993	2.76809554471551
1994	3.1932856693890255
1995	2.844437502654832
1996	3.0732324208286723
1997	4.147559826301257
1998	3.914095608573797
1999	4.259875780144496
2000	3.891929608321247
2001	3.978216571519987
2002	4.969634555626976
2003	4.60359440112952
2004	5.450136370892527
2005	5.590334107189309
2006	5.6618643691366115
2007	5.47774448153161
2008	5.333195567331709
2009	5.528251201350294
2010	6.791633718788533
2011	7.417247551597428
2012	7.762863040999432
2013	7.993378792295889
2014	8.598302509850066
2015	9.604868659306563