Year	% of total
1960	49.48641465539069
1961	51.56980203235628
1962	54.34853530252691
1963	53.43210043568506
1964	57.24221388639482
1965	56.75551117226618
1966	55.792235291042125
1967	58.252107127199814
1968	59.714307907003025
1969	62.049988076790896
1970	63.86566459622935
1971	73.65507339152622
1972	73.42957682434266
1973	74.71359665087337
1974	73.58426270840437
1975	71.32762618132533
1976	74.79955831761188
1977	69.20531782043025
1978	69.72689167061881
1979	68.97038817806084
1980	68.6723633631175
1981	64.51333268799796
1982	63.71300797857414
1983	61.38583786731155
1984	57.40563558722883
1985	54.38573291097468
1986	53.55153768418867
1987	52.54453725954809
1988	50.63862680453482
1989	52.83118065578726
1990	53.17067102738701
1991	52.555596157861764
1992	51.62805181699807
1993	50.33636534666894
1994	50.63955654888178
1995	50.88386014884833
1996	50.67390774299435
1997	50.08659620987736
1998	50.7161437545997
1999	50.58839601100681
2000	50.63903561125749
2001	49.6885336965691
2002	51.2634881033186
2003	52.347793433653024
2004	51.1443288472478
2005	51.662594541348824
2006	51.75353079675734
2007	52.338189825171696
2008	50.72941428367993
2009	49.20487524647501
2010	47.5561848490158
2011	47.56187913437035
2012	45.679238865816984
2013	42.7303553450239
2014	40.21366515051991
2015	41.528917695120256