Year	% of total
1971	6.572265936510862
1972	7.34267233921109
1973	7.4622503164549965
1974	7.181959554601873
1975	7.032217226459456
1976	5.856478266695808
1977	6.045924126989242
1978	5.728548775448718
1979	6.37388838268582
1980	6.9225311691049045
1981	6.356360003979066
1982	6.902772546486768
1983	7.418254058155198
1984	7.618740469861781
1985	7.389122097032355
1986	6.83007175514361
1987	6.845329512441587
1988	6.557985603409902
1989	6.258299816264177
1990	6.193323160230492
1991	6.128830905600119
1992	7.033078825656935
1993	7.00942025046566
1994	7.010863044122699
1995	7.103803159868782
1996	8.286659672267053
1997	8.518275465528875
1998	7.915570205824479
1999	8.490785853901075
2000	9.10836337751697
2001	8.321697552380273
2002	8.03631257003381
2003	6.443630841089727
2004	5.9673321703857125
2005	6.032179381953491
2006	6.316701450290411
2007	6.488570561643406
2008	6.548869256068864
2009	6.35002097488691
2010	5.6266097018387855
2011	5.458476229549366
2012	5.4370381505264955
2013	5.318985554717734
2014	5.033613380801595
2015	4.8099034108758145