Year	% of total
1960	53.315649867374006
1961	48.471259682022016
1962	45.156537753222835
1963	39.965635738831615
1964	33.55010345846882
1965	29.043619615280413
1966	28.164794007490634
1967	27.907509157509157
1968	37.13756940160395
1969	39.24026590693258
1970	32.36055948886203
1971	29.743020304568528
1972	25.968935984903467
1973	24.918345127925967
1974	24.0859651421832
1975	25.289190267251694
1976	27.347135291285507
1977	24.975058197539077
1978	21.127928675098488
1979	17.11466165413534
1980	16.401665720234714
1981	15.41456928483237
1982	16.885090218423553
1983	17.89688427299703
1984	20.229619081523673
1985	21.4973170939443
1986	26.35085723571951
1987	55.00831419748199
1988	58.355951919348584
1989	58.7631151174819
1990	41.591116733431726
1991	39.20294708640321
1992	42.19264892268694
1993	40.98086568827791
1994	39.71951509389113
1995	39.86593955919109
1996	36.95560253699789
1997	34.47102442988471
1998	32.28278570744324
1999	26.795313576843554
2000	28.796519241329786
2001	28.67002273465411
2002	27.45642635752526
2003	24.950726036764408
2004	24.703549474519136
2005	24.93170998204948
2006	21.699365688154597
2007	19.747190002513737
2008	17.20275511568811
2009	14.325059017097075
2010	12.617120954003408
2011	14.522897953173317
2012	18.510740208540586
2013	16.746823069403717
2014	15.332455052696838
2015	17.345813018256877