Year	% of total
1960	0.4607154971955543
1961	0.4684793981558969
1962	0.44341950306728717
1963	0.44779858825775243
1964	0.4147312175733183
1965	0.42239887736780624
1966	0.5410292944674371
1967	0.5549399391260462
1968	0.5710182249151832
1969	0.5658174991505899
1970	0.754882657263244
1971	0.7356413860141636
1972	0.6697387677804549
1973	0.6604558513988281
1974	0.5246507146025504
1975	0.5589442924708914
1976	0.5139069022186227
1977	0.519713959557631
1978	0.5223940554884903
1979	0.5075603841862987
1980	0.6139520726249835
1981	0.6177577391769912
1982	0.5515220800261882
1983	0.5584440078972234
1984	0.5678343088658281
1985	0.5819778894535095
1986	0.6163400078136471
1987	0.5792082940431142
1988	0.600523700516641
1989	0.5938104711405235
1990	0.8079845804739716
1991	0.8374660680726665
1992	0.9015022409445735
1993	0.9961892011323017
1994	1.0601328597726116
1995	1.1505453364818978
1996	1.137877646512715
1997	1.4071783552109762
1998	1.6456622797318405
1999	1.780761499580414
2000	2.159279497846573
2001	2.323938251888447
2002	2.8396837335583647
2003	3.292721639060762
2004	4.0473111807883555
2005	4.686363457389819
2006	5.315929132271633
2007	6.336984719092613
2008	7.205804476640665
2009	8.543497228941357
2010	9.478244163006249
2011	11.606086041036779
2012	13.633349948776699
2013	15.178921454685234
2014	16.504375815541184
2015	18.04195965128467