Year	% of total
1971	6.98226721864747
1972	8.48187412284704
1973	7.93193358723366
1974	6.91612687537119
1975	5.0714051772918
1976	4.79388247887584
1977	3.25714661286364
1978	4.02176972729123
1979	4.88336396571048
1980	4.53630254347219
1981	5.42588893434929
1982	6.92025693359707
1983	8.1357177701324
1984	8.70537291976303
1985	7.91152511046923
1986	9.03490646373931
1987	8.90296095571451
1988	9.58479087165884
1989	8.2052257388642
1990	9.60180465329286
1991	8.09592454943325
1992	8.89282291253402
1993	9.74543230723006
1994	11.5853216912824
1995	12.5613537593472
1996	14.239243557005
1997	16.0857317033039
1998	15.5640498124294
1999	15.0978617694592
2000	14.5797663734562
2001	13.5719772848691
2002	13.5595552152164
2003	13.0675456180877
2004	14.6038280068707
2005	15.4617023184896
2006	16.0786552448303
2007	18.2309672147723
2008	19.4774568747882
2009	16.8623325620248
2010	13.5426129227789
2011	12.9921041372259
2012	12.4655774653283
2013	10.1741557005424
2014	8.2225758096702
2015	8.58253151053153