Year	% of total
1971	15.767143372918236
1972	18.537714296894436
1973	17.900609034942548
1974	12.972703321051565
1975	14.90568700816246
1976	15.052764938519061
1977	18.40957988273505
1978	22.431773588643594
1979	17.354610504227942
1980	14.519280181766625
1981	12.003755888084905
1982	13.308242265052336
1983	16.855207174321166
1984	20.389212697325313
1985	15.523884290352797
1986	17.256667052603532
1987	17.649829765120707
1988	16.842086864634677
1989	13.768964981542029
1990	12.228072088528691
1991	10.94811064775566
1992	12.89891165452054
1993	13.261491882688519
1994	12.548914614183438
1995	15.134629281030165
1996	13.674044176371286
1997	5.1299562155023075
1998	6.506717404071936
1999	5.44983837212452
2000	5.282660101153184
2001	5.541950144840994
2002	4.619329311038557
2003	4.9753573025058815
2004	4.955772234070589
2005	5.928582642622824
2006	6.384206776793458
2007	8.109123458849412
2008	7.787557607184666
2009	8.308141562568396
2010	7.132258570083715
2011	6.632931353077962
2012	6.946643484299879
2013	6.893667905277316
2014	7.42563871711695
2015	7.8202482126588535