Year	% of total
1971	71.85989717860555
1972	68.68549457185973
1973	69.00118060194558
1974	66.05784531100674
1975	66.33985858803447
1976	65.53780795999016
1977	64.39811780554449
1978	66.54738137622088
1979	66.21365061791353
1980	68.35127165441845
1981	69.77371551062393
1982	70.63748947633516
1983	72.80124279087828
1984	72.56960959719197
1985	70.93641170958797
1986	68.98105918670856
1987	71.96679688834998
1988	68.75826849462906
1989	68.61546692098266
1990	70.00198989244966
1991	68.8373935264589
1992	69.76094426312154
1993	71.5788305441549
1994	71.28491334015138
1995	70.69372938042092
1996	71.30219380178839
1997	71.39760830858776
1998	69.73344274040365
1999	69.26742321210563
2000	68.88954677599205
2001	68.26540939298246
2002	67.76847893420138
2003	69.05755566464788
2004	69.19446003598023
2005	69.29827301641104
2006	68.91673049475229
2007	69.51368667877679
2008	68.63924079257518
2009	67.54111014095196
2010	66.90162394886244
2011	66.8667160115156
2012	66.98893899009568
2013	65.84962367941829
2014	64.55522717095322
2015	64.740097339609