Year	% of total
1971	15.709312241582035
1972	16.183508612312465
1973	16.549378119811788
1974	17.683804032036733
1975	17.08575282150188
1976	17.597166161924157
1977	17.566906432479858
1978	16.482681453892326
1979	17.055047846700305
1980	17.45551694304023
1981	18.034215838010166
1982	18.242210793101133
1983	18.32978403935741
1984	18.301733790753616
1985	18.205119253523332
1986	17.723942818885224
1987	17.5664387582228
1988	17.725546140779926
1989	17.244194479934485
1990	24.153924359548263
1991	24.122747590884217
1992	24.428304238804603
1993	25.81190216155071
1994	26.465718037437618
1995	27.086371528481575
1996	26.21651115578554
1997	26.04185084248635
1998	26.30049765972615
1999	25.483568931926115
2000	25.055892577841345
2001	24.58512888929597
2002	23.996494126498657
2003	22.214177737508805
2004	22.93480571142342
2005	22.51751182384469
2006	21.839922864618067
2007	20.9274192859251
2008	21.51741386347427
2009	21.62570068132324
2010	21.532640365506246
2011	20.026362363439727
2012	21.108743300152515
2013	20.46123512904646
2014	20.93081335521449
2015	21.054807445140842