Year	% of total
1971	4.487068454784119
1972	4.19647712729534
1973	4.117997633599145
1974	3.953717622889552
1975	4.055414781120647
1976	3.913674239825079
1977	3.605951721115127
1978	3.2952768513986186
1979	3.419967813506813
1980	3.81864135872036
1981	4.073874945641872
1982	4.531206295121594
1983	4.385248835154176
1984	4.461913674478934
1985	4.296403133739054
1986	4.253130306418487
1987	4.567110033646824
1988	4.876295859722298
1989	5.175810089643115
1990	21.26023581707225
1991	20.856928056628448
1992	19.966556684508635
1993	19.304455986594864
1994	18.093919426770476
1995	17.819455357319818
1996	18.077106269902153
1997	18.211075292122192
1998	18.43040442378025
1999	19.252314375888076
2000	19.299982490755013
2001	19.857567191459378
2002	20.006890231415053
2003	20.454647155854396
2004	20.202004643223013
2005	19.83696447045969
2006	19.246432996465863
2007	19.244526407523814
2008	19.482081406785216
2009	19.322763222031185
2010	19.37777646320518
2011	17.979486402279505
2012	17.778335929409224
2013	17.039982171678012
2014	17.352850817764608
2015	17.61464687203388