Year	Percent
1991-01-01	18.1919994354248
1992-01-01	16.1509990692139
1993-01-01	15.7659997940063
1994-01-01	17.4479999542236
1995-01-01	17.9580001831055
1996-01-01	15.7620000839233
1997-01-01	16.3080005645752
1998-01-01	15.8500003814697
1999-01-01	16.1779994964600
2000-01-01	17.4370002746582
2001-01-01	17.5389995574951
2002-01-01	17.5960006713867
2003-01-01	15.5909996032715
2004-01-01	15.6780004501343
2005-01-01	17.1630001068115
2006-01-01	16.9790000915527
2007-01-01	17.1499996185303
2008-01-01	16.7259998321533
2009-01-01	16.8290004730225
2010-01-01	16.5669994354248
2011-01-01	16.4009990692139
2012-01-01	16.0139999389648
2013-01-01	16.3150005340576
2014-01-01	16.6170005798340
2015-01-01	16.4130001068115
2016-01-01	16.1490001678467
2017-01-01	16.7450008392334