Year	% of total
1971	33.23969151485741
1972	31.714651716780157
1973	31.59508656195642
1974	30.31729998209543
1975	30.548228676679486
1976	31.398785566793354
1977	31.263188580101044
1978	30.55719936430945
1979	31.406420395118666
1980	32.95347008434713
1981	33.12812157185526
1982	33.759165821653234
1983	34.14114731004511
1984	33.88044820227901
1985	34.800269583156634
1986	34.59385246783644
1987	35.02083407540641
1988	34.74409892090702
1989	34.22514351833456
1990	36.9852641019274
1991	37.05310148680479
1992	37.38813775741731
1993	37.35687914355101
1994	37.50654155908699
1995	37.33092349031498
1996	37.943686012320676
1997	38.0006216916544
1998	37.800853587404866
1999	37.62614327586613
2000	38.61392538943606
2001	38.42604457550146
2002	38.72941575901649
2003	39.80907642653481
2004	39.35816363828481
2005	39.83362135925413
2006	40.49190928505102
2007	41.11453354892546
2008	40.61188871889238
2009	39.99521942716684
2010	40.087189014091656
2011	40.978070522295155
2012	40.25463625625439
2013	41.02197692471742
2014	40.46540483992606
2015	39.14569166025153