Year	% of total
1971	21.57311127410795
1972	22.127493410562625
1973	22.52666148948657
1974	25.211217232746442
1975	22.695178535404477
1976	22.097305679395234
1977	21.03439742637961
1978	17.384389909258164
1979	17.769107997871963
1980	19.36267172271563
1981	21.195072266951207
1982	22.705078125
1983	24.57318461188254
1984	22.994779935875354
1985	22.491416883780953
1986	21.02862990234245
1987	20.111810485249464
1988	20.01980888098164
1989	20.244181871035035
1990	20.396994533759987
1991	18.460062719055525
1992	17.567311300925244
1993	18.10820385043398
1994	18.03403196354411
1995	18.908061600493692
1996	17.400392505369176
1997	17.253725719437128
1998	17.815845824411134
1999	16.437016050138435
2000	16.40538216085999
2001	18.733393249868836
2002	17.409035621619136
2003	14.846539718592913
2004	16.04464166585735
2005	15.877720392918759
2006	15.2056173965109
2007	14.786564649170117
2008	16.877870664530448
2009	16.571464102473687
2010	16.94897365007753
2011	14.624130234665806
2012	17.308733949989687
2013	16.731349029635798
2014	18.55249397916779
2015	19.069812965357887