Year	% of total
1971	13.346619036042695
1972	13.570023216724108
1973	14.199964616567296
1974	13.314691819834165
1975	13.472180814998696
1976	12.879610055816723
1977	13.43313677228189
1978	13.133423078922648
1979	13.459312363509715
1980	13.090819180461736
1981	12.76425125345316
1982	12.994379083808797
1983	14.692171122264167
1984	14.152498490941499
1985	13.77701443349008
1986	12.721288834756006
1987	12.080950968158124
1988	11.634786550917687
1989	10.725391930360676
1990	15.187466759282623
1991	14.996585956188223
1992	14.0380879689118
1993	13.346124943725668
1994	12.00627243866466
1995	12.458360545180824
1996	12.481240414234037
1997	12.76450835480728
1998	12.01047595849856
1999	11.216269008757976
2000	12.104348603588049
2001	11.046350667131057
2002	10.82201023552071
2003	9.394154292362787
2004	9.650005198597938
2005	9.59830463400154
2006	9.907873008143762
2007	9.873307409786308
2008	10.265329081274285
2009	9.949959442334052
2010	9.118388559953276
2011	9.627005172046104
2012	9.134993497619403
2013	9.551943594966968
2014	8.362045775735364
2015	7.405722974772806