Year	% of total
1990	37.142397942783674
1991	38.85750156936598
1992	32.169475048606614
1993	33.11568725933367
1994	35.742535866614965
1995	37.00921551924417
1996	35.59010492456154
1997	38.091985428051004
1998	36.72785547785548
1999	35.4094405067109
2000	34.94568408690546
2001	36.34038434950919
2002	37.86820112344157
2003	37.67727930535456
2004	35.747495252439265
2005	38.923066746047496
2006	36.70525967581872
2007	37.858139998670474
2008	38.2523324592963
2009	34.987502286167164
2010	34.80159950784374
2011	39.0512095507383
2012	35.554412143040906
2013	33.52520716047821
2014	37.114723533181845
2015	38.11837753931295