Year	% of total
1971	0
1972	0.0011869872915752414
1973	0.08593594402711567
1974	0.49211454733655646
1975	0.8892027744972056
1976	1.6401095998821855
1977	1.7237909989960691
1978	1.6085191768993585
1979	2.25008896500382
1980	2.770373545351239
1981	3.70506877360025
1982	4.228620888007779
1983	5.172167468970349
1984	5.857346632230918
1985	7.308704728596199
1986	8.419843831875372
1987	10.058250070015186
1988	11.558584756335774
1989	11.518227150413143
1990	17.33297122390665
1991	17.462052595415077
1992	17.29178688209271
1993	17.49017593424939
1994	17.295983956394302
1995	17.55955229337986
1996	18.075093470225674
1997	18.644697958243782
1998	18.88872220198167
1999	18.54666627692847
2000	19.153293913930888
2001	19.999634693187936
2002	21.786438509660535
2003	21.43751180286255
2004	21.28337516744482
2005	20.777987595680184
2006	20.410989219436626
2007	19.719458455449196
2008	21.325406790087044
2009	22.121614409900626
2010	19.352598890753725
2011	19.650031996475143
2012	20.276552141915026
2013	20.03117071246419
2014	20.54993138245502
2015	13.65341674231701