Year	% of total
1971	3.777543962692124
1972	3.89664887446597
1973	3.7738015686214883
1974	2.859543487539255
1975	2.921440822514664
1976	2.9419596519404685
1977	3.250155805971205
1978	3.4356462661779656
1979	3.2499240989125058
1980	2.8626755877815855
1981	2.4094609613576483
1982	2.4740847484342896
1983	2.705574979391988
1984	2.738931271508415
1985	2.3772426440660714
1986	2.6980265428304837
1987	2.848995279009144
1988	2.6691742728544967
1989	2.220601701816315
1990	2.198368847437516
1991	2.082758150549046
1992	2.3900834104120463
1993	2.4045787512623384
1994	2.5283939670235878
1995	3.042423768588678
1996	2.7111409248063234
1997	1.9228655820457918
1998	1.8668634104984805
1999	2.207326723281529
2000	2.3896183001650657
2001	2.227336489614482
2002	1.9934295135778384
2003	2.073010712379544
2004	2.3976071925926363
2005	2.568136475040057
2006	2.778112817346402
2007	3.232874622188243
2008	3.339198409744857
2009	3.4917367943531183
2010	2.6615245509578305
2011	2.874007708580716
2012	3.4142118416254856
2013	3.6877922686781273
2014	3.846291530840238
2015	4.030005991248011