Year	% of total
1971	11.830348607924034
1972	11.06277342958157
1973	10.639932055842072
1974	9.756592854539607
1975	10.37751847473446
1976	9.480855961789656
1977	9.510603556519323
1978	9.3841296114569
1979	9.866771835625
1980	9.578782587784335
1981	8.946832449497306
1982	9.592233550512317
1983	9.468271170993896
1984	9.398776962791864
1985	9.089157020101847
1986	8.991678533124523
1987	8.521154173505641
1988	9.66360160430877
1989	9.611743311199387
1990	9.718841270132765
1991	10.360646940948863
1992	10.106937117935692
1993	10.197203276222309
1994	9.98959923726116
1995	10.67225255947452
1996	10.829592013429638
1997	10.8293500215061
1998	12.083929174343751
1999	12.920599391758431
2000	13.991585591395324
2001	16.164526353747867
2002	17.424851120984684
2003	19.40447024885719
2004	20.503746329318794
2005	19.49657496150191
2006	19.788612041759418
2007	20.19719852600303
2008	21.75713011098291
2009	21.331518335554847
2010	22.98175180361792
2011	21.86898613930951
2012	23.568427069457165
2013	24.877320734788537
2014	25.943750714826635
2015	27.214419235851718