Year	% of total
1971	27.165590183685513
1972	26.295345542990894
1973	25.135183440398833
1974	24.90478895100198
1975	24.885437970442766
1976	23.63248179697968
1977	23.789045742537
1978	23.99247263305804
1979	23.20268664492029
1980	22.550227582907606
1981	22.02894838254562
1982	22.37743389936829
1983	22.40588624726425
1984	23.05373001466395
1985	24.595740255859223
1986	25.249395038264655
1987	25.951550439752964
1988	25.630251259661783
1989	26.16455948061469
1990	35.970907196887715
1991	36.70647308579979
1992	38.23002871827906
1993	38.634371822585535
1994	40.279437324006885
1995	40.71619685561756
1996	41.51107970990143
1997	41.633439480020805
1998	41.15603047850112
1999	41.82200001625379
2000	42.71665653252092
2001	43.05209188961731
2002	44.013821508998525
2003	45.544637093305546
2004	45.58600067305289
2005	46.89734325058878
2006	48.666457618303184
2007	50.06920290052592
2008	49.64458455818816
2009	49.935846854670636
2010	50.10989129536999
2011	52.16089027258083
2012	51.517067834472805
2013	52.19650593248193
2014	51.3322184488312
2015	50.76091901974974