Year	% of total
1971	54.607682839795615
1972	58.00316115167657
1973	55.07727492604813
1974	58.70247446452675
1975	56.38712820137942
1976	57.34789929319898
1977	57.28316245933222
1978	52.26036242210177
1979	54.52435150445423
1980	56.09094363884775
1981	57.50074974307425
1982	61.38792717363704
1983	61.46664915164052
1984	62.1786093773228
1985	66.02046807365174
1986	67.0338359557402
1987	71.73702266961129
1988	69.9120968915124
1989	71.48577317072852
1990	70.10127525986016
1991	71.9743940528099
1992	73.5032253783932
1993	75.4867443710397
1994	73.64272258863006
1995	76.97498900103203
1996	78.95216486257426
1997	78.71435934561902
1998	78.06384129406914
1999	79.8654288394687
2000	81.2186078021801
2001	81.09573587734849
2002	82.02023032688831
2003	80.75466694324032
2004	80.4855998318093
2005	78.4172804320626
2006	77.67854313064981
2007	78.09393496092184
2008	79.71006617568543
2009	80.30142725124892
2010	78.96399709405767
2011	77.93627155440242
2012	79.55458539941634
2013	77.92529879466726
2014	79.15077993814776
2015	79.9771841263565