Year	% of total
1971	5.648175400550382
1972	6.669671258554269
1973	7.825525203124513
1974	7.354748167262202
1975	7.479457212339614
1976	9.16419513202162
1977	8.711266261129472
1978	9.08141837664218
1979	9.591202823765869
1980	9.251446200148079
1981	9.144232741551868
1982	8.199035516588909
1983	7.742827504407747
1984	6.9862356465276925
1985	5.5971029322133425
1986	5.753788466569447
1987	5.193599089538459
1988	5.105446853233161
1989	4.829860870653134
1990	10.621938717850066
1991	10.299574050371016
1992	9.400832944521994
1993	8.848993715272162
1994	8.025191674542977
1995	7.88085678353714
1996	7.296031930657762
1997	6.867149564416769
1998	7.236815691003226
1999	6.720884105274641
2000	5.652770065733899
2001	5.129693135875823
2002	4.960879623424415
2003	4.478730412347411
2004	4.368031390555665
2005	3.774002072718897
2006	3.267140307449185
2007	2.8199163334832007
2008	2.5451196481969225
2009	2.267043302826721
2010	1.9645816289529865
2011	2.065903130966185
2012	2.0225603882121295
2013	1.6285104874991103
2014	1.730512243801511
2015	1.570910128210818