Year	% of total
1971	20.20095438398132
1972	19.71790352933899
1973	18.5848097845856
1974	20.274522664974644
1975	20.035373512991068
1976	18.453434073842338
1977	18.057596762324042
1978	18.3826477492567
1979	18.589474120936963
1980	18.26256327252212
1981	18.40273936858235
1982	18.924394463271526
1983	19.02726302784262
1984	18.390681322306733
1985	17.843518232364175
1986	17.64547626125667
1987	16.873629129241987
1988	16.623029898529925
1989	15.702965061351936
1990	17.918715929084204
1991	18.07549890192371
1992	17.904517213636908
1993	18.517732917416595
1994	18.233558066140905
1995	18.525853463667755
1996	18.19636040088214
1997	18.033549100846923
1998	17.65353188121577
1999	17.20445626317374
2000	16.798580950785738
2001	16.30024342994516
2002	16.097353256422227
2003	15.59972704301395
2004	15.88429950880445
2005	15.888623634632204
2006	15.865373440226115
2007	15.393423015651306
2008	15.729530971913135
2009	16.06135825696833
2010	15.872421343472206
2011	15.694731778802026
2012	16.05285683708279
2013	16.13887328046099
2014	16.234791008698856
2015	15.889553840668016