Year	% of total
1990	37.51793882332864
1991	37.43939408245237
1992	37.062936271323714
1993	36.4022974078101
1994	34.10807677720427
1995	33.704530224567314
1996	34.78800598518798
1997	35.047933565598676
1998	34.323468296595024
1999	35.769193826062384
2000	36.40245639151661
2001	37.207520933305354
2002	37.70123514243265
2003	38.75522302831635
2004	39.28314956711082
2005	39.90636524476058
2006	39.456515931808084
2007	41.11024393578597
2008	40.92354787806468
2009	40.49061480448213
2010	41.61288511335412
2011	41.225178178368324
2012	41.27106001296204
2013	41.61038627323574
2014	42.94912078423885
2015	41.42842200501018