Year	% of total
1971	71.80487547837902
1972	68.63290344884642
1973	68.94834776439056
1974	66.00726612699708
1975	66.28906347204328
1976	65.48762695828184
1977	64.34880944201812
1978	66.49642736414036
1979	66.16295213686577
1980	68.2989364392744
1981	69.72029115838787
1982	70.58340374947888
1983	72.7455003209579
1984	72.51404448422095
1985	70.88209710389725
1986	68.92824175572271
1987	71.91169333713262
1988	68.7056216500642
1989	68.56292941675484
1990	69.94839075503992
1991	68.78468609742407
1992	69.70752968957676
1993	71.52402405108435
1994	71.23033189366352
1995	70.63960059178378
1996	71.24759912399325
1997	71.34294057379424
1998	69.68004922423019
1999	69.21438651785637
2000	68.83679941424683
2001	68.2131399208716
2002	67.7165899519021
2003	69.00467966182372
2004	69.14147920819003
2005	69.24521270107753
2006	68.86396231897193
2007	69.46046142546784
2008	68.58668508516466
2009	67.48939525043505
2010	66.85039870025905
2011	66.81551749122856
2012	66.93764688609431
2013	65.79920392658843
2014	64.50579851189694
2015	64.69052712912556