Year	% of total
1960	0.16896831682242788
1961	0.25406514604670905
1962	0.3401866952146154
1963	0.5063127086437699
1964	0.6552619402453924
1965	0.9654732411676423
1966	1.2265685618625166
1967	1.380261993611593
1968	1.6049774366421385
1969	1.7520383345064874
1970	1.9984844153660875
1971	2.67201374451158
1972	3.3771129840025225
1973	4.168160577035071
1974	5.292133003008742
1975	7.188677637059547
1976	7.730241227090966
1977	9.23265849255272
1978	10.331189535250775
1979	10.225668519350416
1980	10.815203383673321
1981	12.579073148126557
1982	13.591213557446572
1983	14.774654032673382
1984	16.86230622338205
1985	19.37132691568218
1986	20.843732782827924
1987	21.53419143811917
1988	22.407390885324478
1989	21.932774047663077
1990	22.561372527869306
1991	23.205143663376656
1992	23.310486119377742
1993	23.569290321664248
1994	23.65891240951892
1995	23.893088471769293
1996	23.880553711943218
1997	23.236171556616917
1998	23.277380532481054
1999	23.523612111900814
2000	22.95771177442592
2001	23.56530567948377
2002	22.94450962052993
2003	22.17383103009111
2004	22.548721622252383
2005	22.236790857403673
2006	22.14926382565406
2007	21.006603041563434
2008	21.001727071378557
2009	21.423975165426416
2010	20.841846776422003
2011	19.09602253428749
2012	17.87694825487093
2013	17.953316059113913
2014	18.168086535969895
2015	18.033114680449312