Year	% of total
1971	3.7804385696407907
1972	3.8996347475676316
1973	3.776693307897405
1974	2.8617346610982644
1975	2.9236794259534302
1976	2.944213978279304
1977	3.252646292825396
1978	3.4382788882343758
1979	3.252414408217245
1980	2.8648691613653776
1981	2.4113072515690055
1982	2.4759805577154363
1983	2.707648171977656
1984	2.7410300239170518
1985	2.3790642464469154
1986	2.700093951298975
1987	2.851178369824973
1988	2.6712195727831585
1989	2.2223032754259893
1990	2.2000533847465125
1991	2.084354099206299
1992	2.3919148522472713
1993	2.4064213003976405
1994	2.530331391661977
1995	3.0447550772559833
1996	2.713218382391799
1997	1.9243390103182663
1998	1.8682939261598766
1999	2.2090181247143903
2000	2.3914493856016983
2001	2.2290432238692084
2002	1.994957012656253
2003	2.0745991918974487
2004	2.3994443996532033
2005	2.5701043530473546
2006	2.780241593277191
2007	3.2353518670430974
2008	3.341757127000114
2009	3.4944123967253695
2010	2.663563989157715
2011	2.876209965593725
2012	3.416828039191578
2013	3.690618101873344
2014	3.849238816775687
2015	4.033094051495795