Year	Percent
1991-01-01	38.1980018615723
1992-01-01	37.7820014953613
1993-01-01	39.0470008850098
1994-01-01	39.7350006103516
1995-01-01	39.6080017089844
1996-01-01	40.5670013427734
1997-01-01	41.3019981384277
1998-01-01	41.4599990844727
1999-01-01	42.1160011291504
2000-01-01	41.7389984130859
2001-01-01	41.4280014038086
2002-01-01	41.4160003662109
2003-01-01	41.5470008850098
2004-01-01	42.1199989318848
2005-01-01	41.9920005798340
2006-01-01	42.4000015258789
2007-01-01	41.8190002441406
2008-01-01	40.7120018005371
2009-01-01	38.5540008544922
2010-01-01	37.4000015258789
2011-01-01	37.0820007324219
2012-01-01	37.2200012207031
2013-01-01	36.7849998474121
2014-01-01	36.4309997558594
2015-01-01	36.7060012817383
2016-01-01	36.7989997863770
2017-01-01	37.1119995117188