Year	% of total
1971	6.323812966979996
1972	7.128878552385275
1973	7.015495356887741
1974	6.635540833094239
1975	6.244908409561716
1976	5.500183025675888
1977	5.764798641436196
1978	5.8186308783335905
1979	6.727470949557262
1980	7.2793561943044125
1981	6.18907277261392
1982	6.149898927071995
1983	5.992957978215801
1984	6.859978706197893
1985	6.377696333953119
1986	5.640017453461522
1987	5.566371920716043
1988	5.047888015717093
1989	4.710872716302821
1990	4.547504201795499
1991	4.21104066955672
1992	4.392596261355177
1993	3.937424656015741
1994	4.029292781969893
1995	3.971580984751924
1996	4.48004767160763
1997	4.4192875488175885
1998	4.176269625271215
1999	4.544405152353556
2000	5.119117832919072
2001	4.554967857986878
2002	4.574759787846723
2003	4.776311119373975
2004	4.132949117751549
2005	3.5444403456409224
2006	3.0710120653825874
2007	2.9977063078355877
2008	3.01218240005658
2009	2.6490730424658397
2010	2.490565806562278
2011	2.2451551181160987
2012	2.0378451875207584
2013	1.9563340923899535
2014	1.7674358922826476
2015	1.6595035155357467