Year	% of total
1971	3.012951383846514
1972	4.075515544921565
1973	3.454222502792715
1974	3.257007741166652
1975	4.646734276205863
1976	3.5281226099653944
1977	3.790549155540484
1978	2.9137490865589464
1979	2.187381965131377
1980	3.5135789380367677
1981	3.8758916882366363
1982	5.509329082610906
1983	5.844728995482358
1984	5.887461680047084
1985	6.565702812294423
1986	7.02399882698667
1987	6.949074393683875
1988	7.2233164989413945
1989	7.572861784686173
1990	9.66840519554763
1991	12.24456917653534
1992	13.632683949780578
1993	14.258564226549703
1994	14.16983881660537
1995	18.78687671448552
1996	21.588460794453503
1997	20.7318770320656
1998	20.082663890339457
1999	22.07507890285886
2000	22.598114384279253
2001	20.559435092419236
2002	17.805954588348555
2003	10.286770157604527
2004	10.212562347578471
2005	12.465559384282395
2006	16.804868482306606
2007	18.315031254470853
2008	19.670866121388812
2009	21.62164151730653
2010	18.518588387100188
2011	18.36267194797703
2012	18.18037385441636
2013	19.93028688650971
2014	18.647825193137155
2015	18.612624723477406