Year	% of total
1960	10.333871968272215
1961	10.475954145756216
1962	10.624792728314251
1963	10.76595102127865
1964	10.782746603466142
1965	10.201583400982894
1966	10.801011129982104
1967	10.804371384913509
1968	11.595379903009457
1969	11.88367467767406
1970	12.607884338007203
1971	13.1910789029561
1972	12.843806666190355
1973	11.883166062465836
1974	12.015622716910324
1975	11.663365487548868
1976	11.035757712367381
1977	10.930707257198092
1978	10.72520186569987
1979	11.243402737419906
1980	11.432280779715356
1981	11.175455009318663
1982	10.596907698513977
1983	10.022289080672694
1984	10.748807827435119
1985	10.16108417623129
1986	9.474949523842682
1987	9.824631827182987
1988	9.281275441259695
1989	10.6290899633068
1990	10.926259611631968
1991	10.977493834913865
1992	11.394012370591991
1993	11.907809754022077
1994	12.86268255120363
1995	13.330955482820315
1996	13.221822422094254
1997	14.240868907659662
1998	15.001708640549442
1999	15.943960202123694
2000	16.37963653978605
2001	17.320110784311378
2002	18.04305469422657
2003	18.114006610541384
2004	19.079041064994712
2005	19.694312393786827
2006	20.758174365678915
2007	22.023616888945146
2008	22.621109594058453
2009	23.372684929710452
2010	24.296566869267853
2011	25.053588522889335
2012	26.281232631751532
2013	25.397720974320087
2014	25.368783730477052
2015	27.68328417439455