Year	% of total
1971	15.504835055692029
1972	21.284283581661356
1973	25.377767425985848
1974	23.96782028847336
1975	26.07849913522027
1976	31.038935549776557
1977	27.76238742431627
1978	27.970266168263535
1979	30.40878576013689
1980	32.19963548851928
1981	30.170420828385048
1982	27.030770219813167
1983	25.271564475608482
1984	22.73198440527973
1985	17.214560416841188
1986	15.006524144330097
1987	14.437037125581643
1988	14.209976246999895
1989	13.02547011371233
1990	12.856413638156328
1991	12.55229790682875
1992	11.899864735658781
1993	12.416825050696989
1994	9.329272774996486
1995	9.360616653968187
1996	8.602423004354067
1997	8.147471452607109
1998	8.0516289822741
1999	6.57412953118148
2000	5.520023609581145
2001	4.935569892891814
2002	4.787495118885042
2003	4.2858777194638975
2004	4.629503281372837
2005	3.7007051285915757
2006	2.8378104609141865
2007	2.135641195119966
2008	1.8259480400155892
2009	1.40423289522767
2010	1.3575009322209077
2011	1.347969561358645
2012	0.9703215664923563
2013	0.806459382371199
2014	0.7439936035700369
2015	0.5970664325409168