Year	% of total
1971	60.036309459823265
1972	60.093209948149216
1973	60.211834092412644
1974	58.51151480008242
1975	58.72404123922279
1976	56.56098092438485
1977	55.72546697471471
1978	55.361111782300554
1979	55.45022291840266
1980	56.27632308928688
1981	51.808050492260705
1982	53.582587410516034
1983	54.044391588166405
1984	54.268214544105106
1985	55.074896989555434
1986	54.3457320247224
1987	53.97680687717721
1988	53.647693054034754
1989	53.74919277304063
1990	55.65273705981072
1991	55.45078009004549
1992	59.16958389433865
1993	58.897393091049175
1994	58.62498071682006
1995	58.241369917472184
1996	57.45879377828081
1997	58.07971292600552
1998	56.886193323474984
1999	57.315629475899556
2000	59.42132380212184
2001	57.93218079034128
2002	56.165365439838865
2003	57.63815387858532
2004	56.04990614419546
2005	55.25787193087609
2006	56.08717186726101
2007	56.8340859444116
2008	55.197686078551975
2009	53.86489836062681
2010	53.243821191545194
2011	55.05596760488025
2012	53.07206166034396
2013	51.15790789765832
2014	49.61770224940592
2015	50.34462136824579