Year	% of total
1971	54.60768283979562
1972	58.003161151676586
1973	55.07727492604815
1974	58.70247446452675
1975	56.38712820137943
1976	57.34789929319898
1977	57.283162459332225
1978	52.26036242210177
1979	54.52435150445424
1980	56.090943638847754
1981	57.500749743074266
1982	61.38792717363706
1983	61.46664915164054
1984	62.17860937732282
1985	66.02046807365176
1986	67.03383595574022
1987	71.73702266961132
1988	69.91209689151243
1989	71.48577317072855
1990	70.10127525986019
1991	71.97439405280991
1992	73.50322537839324
1993	75.48674437103973
1994	73.64272258863008
1995	76.97498900103206
1996	78.95216486257429
1997	78.71435934561904
1998	78.06384129406916
1999	79.86542883946873
2000	81.21860780218013
2001	81.0957358773485
2002	82.02023032688834
2003	80.75466694324035
2004	80.48559983180932
2005	78.41728043206263
2006	77.67854313064984
2007	78.09393496092186
2008	79.71006617568544
2009	80.30142725124894
2010	78.9639970940577
2011	77.93627155440244
2012	79.55458539941634
2013	77.92529879466727
2014	79.15077993814778
2015	79.97718412635652