Year	% of total
1960	0.06048374777031086
1961	0.18915304545142475
1962	0.23727579472330898
1963	0.32194007267088187
1964	0.31593717195111304
1965	0.3192605234428192
1966	0.4424935745274666
1967	0.5361356910914099
1968	0.9015947681798441
1969	0.8954152828536187
1970	1.3282910037090172
1971	2.3272306814989836
1972	3.099434301637397
1973	4.669299664261204
1974	6.064749942914144
1975	8.566278939762206
1976	9.02697545232767
1977	11.437989071106742
1978	12.18650009350455
1979	11.241603611813497
1980	10.858901829945369
1981	11.635501407067347
1982	12.227421230264886
1983	12.59380831478236
1984	13.31328335127877
1985	15.160755522685593
1986	16.407490392599357
1987	17.416299836739793
1988	19.062672566586873
1989	17.66643719134049
1990	18.571404670797182
1991	19.506170266952306
1992	19.42316016489164
1993	18.87734436987308
1994	19.625519454456516
1995	19.701465812696238
1996	19.121168740946505
1997	17.632467418853256
1998	17.98779501597011
1999	18.978239797609678
2000	18.789422282739977
2001	19.62265203836513
2002	19.011183775608732
2003	18.569953521802685
2004	19.027737643214397
2005	18.457577736346476
2006	18.70318347409973
2007	18.774414768808402
2008	18.764692293883282
2009	19.26677107049617
2010	18.742232793940484
2011	18.430358836254598
2012	18.251404856271296
2013	18.680720063688437
2014	18.807273406740688
2015	18.807551313159866