Year	% of total
1971	0
1972	0
1973	0
1974	0
1975	0
1976	0
1977	0.2670478053183887
1978	7.375436369406538
1979	8.853932584269662
1980	9.33698541851285
1981	7.205213022608003
1982	8.758870182273549
1983	18.35209825997953
1984	21.91495688373476
1985	28.867205682072854
1986	44.308631348305816
1987	54.08298024541903
1988	47.59084759440792
1989	50.552324030097665
1990	50.191229085801595
1991	49.72054213941989
1992	45.44066107199126
1993	40.64599573530954
1994	36.257140031156496
1995	37.004179111069405
1996	36.48675995163002
1997	34.705601627992834
1998	41.509425229903414
1999	43.74607378733085
2000	37.765747281007606
2001	36.27291459773498
2002	36.113267273896014
2003	37.78420762782241
2004	35.65486127022574
2005	37.84192804879935
2006	36.977403236632114
2007	33.56077059438138
2008	34.0044510920493
2009	32.71615051497091
2010	29.915565773738823
2011	29.751390723637783
2012	28.31363537909537
2013	25.801509971351074
2014	28.65300275159105
2015	29.998943968421017