Year	% of total
1971	13.566860904018915
1972	13.235083794407524
1973	12.568713694904291
1974	13.086999723236625
1975	13.306333341850493
1976	11.310911145589033
1977	13.376446974939837
1978	12.691976613567565
1979	12.828528484739133
1980	12.117801912769444
1981	12.30198506920352
1982	12.172019182980486
1983	12.203780526731743
1984	11.738645353867396
1985	11.178253515889661
1986	10.452139955569137
1987	11.078015414736793
1988	11.624980540821074
1989	9.845658465442794
1990	15.612492090439492
1991	15.84336666876663
1992	16.73208546555832
1993	17.701755771324567
1994	18.276339487804748
1995	18.12160202189605
1996	17.062510993862308
1997	17.350154778875055
1998	17.734484332197916
1999	17.68273920576986
2000	17.58866391172485
2001	17.42202411438953
2002	16.0668538820133
2003	14.932721757275527
2004	15.808061395062708
2005	15.601276966457064
2006	15.077206968607634
2007	14.948139933629456
2008	15.111046977051023
2009	15.946427809198449
2010	16.331544268035383
2011	14.885514883548606
2012	15.785531366667904
2013	16.83443838604679
2014	16.596945958013837
2015	16.1809073399382