Year	% of total
1971	71.80487547837899
1972	68.63290344884639
1973	68.94834776439053
1974	66.00726612699705
1975	66.28906347204327
1976	65.48762695828182
1977	64.3488094420181
1978	66.49642736414035
1979	66.16295213686575
1980	68.29893643927437
1981	69.72029115838782
1982	70.58340374947886
1983	72.74550032095787
1984	72.51404448422093
1985	70.88209710389722
1986	68.92824175572268
1987	71.9116933371326
1988	68.7056216500642
1989	68.56292941675481
1990	69.9483907550399
1991	68.78468609742406
1992	69.70752968957675
1993	71.52402405108434
1994	71.23033189366349
1995	70.63960059178378
1996	71.24759912399324
1997	71.34294057379422
1998	69.68004922423017
1999	69.21438651785637
2000	68.83679941424681
2001	68.21313992087158
2002	67.71658995190208
2003	69.0046796618237
2004	69.14147920819002
2005	69.24521270107753
2006	68.86396231897191
2007	69.46046142546784
2008	68.58668508516465
2009	67.48939525043504
2010	66.85039870025903
2011	66.81551749122856
2012	66.9376468860943
2013	65.79920392658843
2014	64.50579851189693
2015	64.69052712912556