Year	% of total
1971	75.89578652859265
1972	72.13923211711432
1973	72.89847192326923
1974	70.15258363628134
1975	70.50046943462237
1976	69.68969963186358
1977	68.37667592773461
1978	69.81017689400836
1979	70.390446050426
1980	72.9195306891863
1981	74.28708956636373
1982	75.11071834039306
1983	75.55873207126643
1984	74.94565251483348
1985	74.30538150306236
1986	72.64358970052666
1987	75.65262870284513
1988	72.40766555917725
1989	72.61354542623256
1990	74.08046170978389
1991	73.47799023150762
1992	74.61612351340686
1993	76.23797652183158
1994	75.28203906474823
1995	74.47305074823034
1996	75.20837578001729
1997	74.98542829584943
1998	72.65943773617072
1999	72.10050805770312
2000	71.50419282651605
2001	71.15746309338601
2002	70.65712466124494
2003	71.55464698617756
2004	71.04659451680776
2005	70.73980078069617
2006	70.09303647218943
2007	69.90798008157977
2008	69.11001635413176
2009	67.47753733031247
2010	67.30660927876743
2011	66.52821974919088
2012	66.180818486467
2013	64.48996758028622
2014	62.322867354447084
2015	61.224502527349145