Year	% of total
1971	30.141499225414865
1972	29.839992657210562
1973	29.26308187264893
1974	27.496988427698632
1975	26.917531157288348
1976	26.50227195457252
1977	26.351306216134375
1978	26.69311923301101
1979	25.53695265896645
1980	25.438654134073364
1981	24.63749011024977
1982	23.911406161412117
1983	23.27424152267681
1984	20.841329603963242
1985	19.29616653596756
1986	20.572416936840558
1987	20.468105810401507
1988	19.833255261273987
1989	19.849501968318574
1990	17.30613297743508
1991	16.614361051390407
1992	16.871627583903248
1993	15.231015109682271
1994	16.228814419393327
1995	14.91480835965406
1996	14.827059603161304
1997	15.679990374706202
1998	17.07655183493732
1999	16.83885385684909
2000	16.371978489960114
2001	16.409624272115394
2002	14.333101428868023
2003	13.109361798706804
2004	12.566028273781587
2005	12.369731581893053
2006	11.543220264448939
2007	11.919194791890954
2008	12.160936547391957
2009	11.410731118727227
2010	10.76606906830473
2011	10.722389632001548
2012	11.264636113469487
2013	10.904207251744955
2014	10.11141702349985
2015	9.912203791577577