Year	% of total
1971	2.008736781594294
1972	1.983030903881808
1973	2.078323753443891
1974	2.1076048629052506
1975	2.3087011582040247
1976	2.2181831836562886
1977	2.2399700944102685
1978	2.1308012579462488
1979	2.557741013383166
1980	2.7003819724494065
1981	2.6697460752847726
1982	3.169056781180113
1983	3.0066400734387564
1984	3.0872886894643017
1985	3.332900168162286
1986	3.2956089046722536
1987	3.8494975200807025
1988	4.320782721905719
1989	4.776283060952505
1990	22.185278266273595
1991	21.753190116987977
1992	20.902778820948235
1993	20.16825764198817
1994	18.906071555111044
1995	18.66864673258277
1996	18.9031073318282
1997	19.25531147205376
1998	19.424530259650155
1999	20.278548425929753
2000	20.295300328107167
2001	20.77873888534764
2002	20.982480449535675
2003	21.536959778041258
2004	21.303043905933773
2005	20.8823090376582
2006	20.202387711050925
2007	20.13775770974342
2008	20.345484738125094
2009	20.230557826925924
2010	20.246865215035474
2011	18.7888343270323
2012	18.516334050877074
2013	17.776226334066553
2014	18.12951200131565
2015	18.378017532981684