Year	% of total
1971	25.59591862916264
1972	25.42015833161213
1973	20.33204710821361
1974	21.65927014109764
1975	20.186880583270963
1976	20.342916395904012
1977	20.247435520529468
1978	20.54097631707901
1979	17.336501791750784
1980	15.742553635274195
1981	14.375796112852154
1982	12.60504589236441
1983	10.577423914330303
1984	9.39390698701291
1985	8.32173713575861
1986	8.51081974323051
1987	8.796277555368475
1988	7.876603244845208
1989	7.87979769716846
1990	7.019424384948057
1991	6.7542881157955525
1992	6.561681531168204
1993	6.162243791884869
1994	5.4098409581953675
1995	5.165160211115062
1996	5.2380415615987514
1997	4.960167591879379
1998	4.6457032539107574
1999	4.2094576129500165
2000	3.6363734358685575
2001	3.8910826222425103
2002	3.653288942951569
2003	4.128201881634578
2004	3.9553821699092913
2005	4.927987951011157
2006	4.782342113308292
2007	4.634185318752655
2008	2.696214514629995
2009	2.6945547691751766
2010	2.9653761375200283
2011	2.9242273600128312
2012	2.888488675476747
2013	3.055193882499637
2014	2.5278234214234048
2015	2.2730759028553837