Year	% of total
1971	17.373809795249574
1972	13.992558712351128
1973	13.962290914854048
1974	10.821777370951482
1975	10.665676903784792
1976	10.551986608806049
1977	11.822789272497259
1978	12.722543042922318
1979	11.320838224085621
1980	8.87819399634471
1981	8.464615528543183
1982	8.270401088198335
1983	11.545487009827287
1984	12.441646555195183
1985	9.341390133707975
1986	9.415042873552478
1987	10.96993785639977
1988	10.482258530937115
1989	9.053646661909264
1990	9.318072543246911
1991	8.724577492415245
1992	10.562544891060107
1993	10.936206933146842
1994	13.130255103272347
1995	14.744765266127843
1996	15.30912491757766
1997	16.954030879618674
1998	17.23800972081317
1999	16.43419322879361
2000	16.094754677636526
2001	16.142935700227344
2002	17.104179263551373
2003	18.575195692301023
2004	20.44673701939173
2005	21.31180071764682
2006	20.957633710214722
2007	21.669028031246526
2008	22.104737371384115
2009	20.915799971467944
2010	20.077559061060466
2011	21.94286051032042
2012	22.180414775310968
2013	21.781924264332194
2014	22.90376961587696
2015	25.75723912868047