Year	% of total
1971	8.651771955011844
1972	8.134515070808407
1973	7.844040921155934
1974	7.024818241323909
1975	8.226391873306241
1976	7.262963275144539
1977	7.045268907107236
1978	6.861827086301833
1979	7.854500774975268
1980	7.712610628955119
1981	6.930401306747862
1982	7.560460184679352
1983	7.023795346413869
1984	6.524823160260651
1985	6.313516962563432
1986	6.1705421924995765
1987	6.051542450697422
1988	7.422353160816185
1989	7.986842753031416
1990	7.896976617902479
1991	8.879732999280222
1992	8.689590001208664
1993	8.587631427485109
1994	8.474096056670216
1995	9.071024434537865
1996	9.352698514673358
1997	9.657763778396268
1998	10.751289223482782
1999	11.922760815377663
2000	13.053055148545505
2001	14.807314772218842
2002	16.57876344969899
2003	18.901340757557108
2004	20.435658086736673
2005	19.897976543482702
2006	20.515331754872545
2007	21.520045767417038
2008	23.733183746332173
2009	23.03125642558983
2010	24.156670537292023
2011	22.87274740756197
2012	24.841130722144857
2013	26.530923065252544
2014	27.810128658505352
2015	29.095378695502372