Year	% of total
1971	31.940788100614732
1972	33.15076096817549
1973	32.15348409316005
1974	34.846421762305276
1975	33.33526763365076
1976	35.36322392413178
1977	34.16155619607559
1978	35.404157001512864
1979	34.89460756362578
1980	31.5644385913318
1981	30.435708867779017
1982	29.138700641491173
1983	29.544737301219747
1984	30.042474839232614
1985	27.8330821514882
1986	27.07497412047268
1987	24.49019222459098
1988	25.537545009899347
1989	25.244838134066732
1990	29.7065506785479
1991	30.370546170652407
1992	31.714406683653294
1993	30.44838210070722
1994	32.18672265771902
1995	30.97660085822589
1996	29.652596970990487
1997	29.249480420143847
1998	29.14255337204174
1999	27.05977413898828
2000	24.675979119509776
2001	25.389713474348298
2002	27.896742943841286
2003	31.235229536738764
2004	29.77938464987767
2005	30.773831023248416
2006	30.253284081672767
2007	28.008649331821683
2008	30.67919182299222
2009	28.048994213531042
2010	31.149352375992954
2011	28.39142996371776
2012	29.210526537743764
2013	28.44580657014261
2014	28.02853609067973
2015	28.13379440049385