Year	% of total
1971	28.72061155527727
1972	28.32572187015537
1973	27.751410404104483
1974	26.01596602545364
1975	25.388051285871388
1976	24.988210557344885
1977	24.836885635617207
1978	25.21914240688411
1979	23.942492638102017
1980	23.888907447555777
1981	22.998799362027754
1982	22.26501398233579
1983	21.638885051065007
1984	19.135126099217842
1985	17.66298116222205
1986	19.004670526455254
1987	18.92202134598511
1988	18.232063228767664
1989	18.205436307954574
1990	15.826385326400064
1991	15.432101303823009
1992	16.18016986135284
1993	14.629627723317828
1994	15.633923441736536
1995	14.25178219172613
1996	14.167243709553857
1997	14.911874839677273
1998	16.463598131221328
1999	16.350207488746488
2000	16.031977394582476
2001	16.060255208367966
2002	14.279890296039117
2003	13.102788811869875
2004	12.549881906509675
2005	12.261882929804138
2006	11.279403640104073
2007	11.719095543401629
2008	11.938821879303182
2009	11.241177776489803
2010	10.589418097066003
2011	10.493662615047954
2012	11.043752166723731
2013	10.624092048035058
2014	9.840572529465819
2015	9.616110241175875