Year	% of total
1971	5.967769566268855
1972	6.939592306147542
1973	8.594886694485245
1974	8.99480043957352
1975	10.351129809007066
1976	12.426619088146525
1977	14.6378272487715
1978	16.4372711377308
1979	17.33392468097883
1980	18.95469166084785
1981	20.494855667798745
1982	22.08604598319589
1983	22.173314747029064
1984	20.05240789513656
1985	20.36797923352384
1986	18.950029690055743
1987	19.7256197012201
1988	19.826707651393434
1989	20.444641463492744
1990	20.517680116166034
1991	21.925511979718124
1992	22.84478997932985
1993	22.04813296737031
1994	17.83639167546122
1995	17.752301010882494
1996	18.830616481398817
1997	19.19587405874935
1998	17.362110243980005
1999	17.775247478889227
2000	18.448298488981216
2001	19.88929350904026
2002	19.760458881310555
2003	21.593076723345476
2004	21.280800869816876
2005	21.656340793221517
2006	19.697810686441475
2007	17.580538360625734
2008	18.42963787845666
2009	15.854143346284486
2010	18.081496573609478
2011	19.081904954604624
2012	18.76894491988155
2013	18.589263136287723
2014	18.876766756620952