Year	% of total
1971	20.174959338831076
1972	18.52980484516496
1973	18.102777417713046
1974	17.079204415610757
1975	16.771485638771612
1976	17.452929625926934
1977	16.640181227943014
1978	16.86659911076201
1979	16.02445111911937
1980	14.333680895945367
1981	13.689671390026215
1982	13.879781468744026
1983	14.539433549696824
1984	15.268151324416543
1985	15.163498221900987
1986	15.01583794975127
1987	14.236585541027475
1988	15.53866197674536
1989	15.237440714993857
1990	23.008609070041842
1991	23.003579856050102
1992	19.54176791724367
1993	19.950726442217146
1994	19.904604262429203
1995	22.228956740886787
1996	21.71210939459946
1997	22.08019177907611
1998	20.952945774988113
1999	19.712548881685933
2000	19.05193872508637
2001	23.13739403613502
2002	22.687983096842988
2003	21.941343452343766
2004	21.200969515185058
2005	22.863760149549194
2006	25.040691837031346
2007	24.89622221668974
2008	25.692979086392576
2009	26.620308066992315
2010	28.40264767497058
2011	28.006478362247634
2012	28.86828651042154
2013	28.59143291589615
2014	28.984653463068895
2015	29.377910628454202