Year	% of total
1971	3.7775439626921252
1972	3.8966488744659715
1973	3.773801568621489
1974	2.859543487539256
1975	2.9214408225146653
1976	2.9419596519404694
1977	3.2501558059712057
1978	3.435646266177967
1979	3.249924098912507
1980	2.8626755877815864
1981	2.4094609613576496
1982	2.4740847484342905
1983	2.7055749793919888
1984	2.7389312715084158
1985	2.3772426440660723
1986	2.698026542830484
1987	2.8489952790091455
1988	2.6691742728544976
1989	2.2206017018163156
1990	2.198368847437517
1991	2.0827581505490462
1992	2.390083410412047
1993	2.404578751262339
1994	2.5283939670235887
1995	3.042423768588679
1996	2.711140924806324
1997	1.9228655820457925
1998	1.866863410498481
1999	2.2073267232815295
2000	2.389618300165066
2001	2.227336489614482
2002	1.9934295135778386
2003	2.0730107123795443
2004	2.3976071925926368
2005	2.5681364750400575
2006	2.778112817346402
2007	3.2328746221882434
2008	3.3391984097448577
2009	3.491736794353119
2010	2.661524550957831
2011	2.874007708580716
2012	3.4142118416254856
2013	3.6877922686781277
2014	3.846291530840239
2015	4.030005991248011