Year	% of total
1960	0.16627340714480396
1961	0.2501911346813213
1962	0.33519058802558854
1963	0.49861476324773235
1964	0.6455925850993529
1965	0.951398528022076
1966	1.208863709249896
1967	1.3609770323848358
1968	1.5824741157021958
1969	1.7274022556250639
1970	1.9700937778357561
1971	2.6358762225691814
1972	3.3327959572557346
1973	4.1113782348113
1974	5.251280547743856
1975	7.176559576137742
1976	7.755531405349872
1977	9.274335970107629
1978	10.368511889333337
1979	10.231981671806947
1980	10.787283825109942
1981	12.571168860429955
1982	13.617180636934306
1983	14.810454369711007
1984	16.888034614671973
1985	19.38687476763165
1986	20.837269255714162
1987	21.549122278163498
1988	22.454813000947134
1989	21.938748596011763
1990	23.490002940912987
1991	24.16893251593742
1992	24.38001948655356
1993	24.77590839347622
1994	24.952775112558783
1995	25.253230635242048
1996	25.402772025831492
1997	24.75902095720628
1998	24.808948981840267
1999	25.004069424470565
2000	24.50750026319173
2001	25.159479787475863
2002	24.50272459905154
2003	23.764898480057546
2004	24.21732823588919
2005	23.92162868072571
2006	23.89441133662337
2007	22.739267527384552
2008	22.74112722201942
2009	23.219943005043557
2010	22.657998343645716
2011	20.918878818689556
2012	19.68594027328511
2013	19.652412571961403
2014	19.993286276352485
2015	18.92125309349055