Year	% of total
1971	67.93499098218658
1972	64.51001880886082
1973	64.91539476279657
1974	63.05170702848207
1975	62.951182117918755
1976	61.9802490026116
1977	60.366120040160496
1978	62.10353998817793
1979	61.488185027985196
1980	63.47906270762898
1981	64.98159475225641
1982	65.72251625329379
1983	67.06801543446241
1984	67.36389178905094
1985	66.03949250426815
1986	64.11252695151241
1987	66.55384547195295
1988	63.770881086903884
1989	63.69435835203062
1990	64.836089918581
1991	64.08302842597676
1992	64.66855714608374
1993	66.40431369904174
1994	65.56129627910038
1995	64.8045368005101
1996	65.51574299856793
1997	65.32570947196822
1998	63.95105320566997
1999	62.79852930724674
2000	62.6061677820691
2001	62.05814959759326
2002	60.80388736591815
2003	62.37936207162092
2004	61.34487926543451
2005	61.137834556174376
2006	60.47462453233848
2007	60.80059033020208
2008	59.964288098243365
2009	58.51844654287629
2010	57.44642624091618
2011	56.57325849432445
2012	55.809247909904656
2013	54.16562678524905
2014	52.10768584432747
2015	51.10213462880663