Year	% of total
1971	15.10131339914979
1972	15.131518987280263
1973	14.627744077964072
1974	12.84694649350401
1975	12.982433103543741
1976	12.74006100601702
1977	12.643820793855804
1978	12.158462970561718
1979	11.057102499269254
1980	10.222233626212454
1981	9.811385812424737
1982	8.943584710792392
1983	8.722162127836784
1984	6.442066397625138
1985	5.568020559087608
1986	6.073924817785985
1987	6.105896921056546
1988	6.405405139815936
1989	6.070135515852296
1990	9.38153471995886
1991	10.689080398681494
1992	9.825699319190603
1993	10.51152262894538
1994	10.355272148958038
1995	10.563399527132225
1996	11.095705065099672
1997	11.32383442493841
1998	11.313913453247809
1999	11.578776519087558
2000	10.83685097275559
2001	10.624994147483587
2002	10.642617877770297
2003	10.802823945499346
2004	10.827482104317422
2005	10.34354244012015
2006	10.424676199867932
2007	9.637610212638235
2008	8.614105880510522
2009	8.452808595670325
2010	7.55893890609652
2011	7.19004363417587
2012	6.861490520835516
2013	6.301167259417928
2014	5.87219292090925
2015	5.211673646018725