Year	% of total
1960	63.8080764142698
1961	64.38282819181258
1962	65.68627773748803
1963	66.40159514722617
1964	67.71180349862838
1965	67.08413323497415
1966	67.37138284192433
1967	68.15801329699195
1968	69.47455981142596
1969	70.295997769971
1970	71.39063963048129
1971	73.36092806218738
1972	73.40431040191213
1973	74.19107353380272
1974	71.12014475654675
1975	69.55020048042829
1976	71.1807355517731
1977	70.3158603987242
1978	68.76153028114707
1979	68.63949946544226
1980	68.58692767030551
1981	66.69495226248232
1982	64.86318335122282
1983	63.50573108878878
1984	62.281184051518935
1985	60.540401344323534
1986	59.35393101275018
1987	59.53666801847377
1988	59.1207023188001
1989	60.126486773936385
1990	58.24794972771765
1991	58.04583718676714
1992	58.04505955103346
1993	57.50124379190796
1994	58.033270029224084
1995	57.43375108232867
1996	57.441968943497315
1997	58.50683016966535
1998	59.410796868816604
1999	59.41532366861465
2000	60.30262140565643
2001	60.58577552198151
2002	60.81994536136281
2003	61.85347883496328
2004	61.140424368566414
2005	61.35835581942079
2006	61.11221920057546
2007	62.21577378165419
2008	61.435817298457685
2009	60.13577770219146
2010	60.25404715286237
2011	60.2915900493084
2012	60.47545988245411
2013	59.24435750205346
2014	58.39788292327203
2015	57.76915022200679