Year	Percent
1979-01-01	26.4285869697482
1980-01-01	25.9650444755844
1981-01-01	25.7956922694511
1982-01-01	25.7057058401403
1983-01-01	25.7833466115027
1984-01-01	25.1627333576195
1985-01-01	24.4647603564740
1986-01-01	22.8187733985938
1987-01-01	22.4292549640605
1988-01-01	21.6727429503674
1989-01-01	20.8216950775191
1990-01-01	19.8917771407606
1991-01-01	19.8736717979610
1992-01-01	20.0969665388294
1993-01-01	20.2806086135351
1994-01-01	20.3104058523600
1995-01-01	19.6228099780942
1996-01-01	19.7007005529600
1997-01-01	19.8333278977285
1998-01-01	19.9794076232388
1999-01-01	20.1509503604904
2000-01-01	19.7225078729311
2001-01-01	19.4470236294705
2002-01-01	19.2029470842283
2003-01-01	18.9023435686678
2004-01-01	19.2054420361560
2005-01-01	18.0707443178114
2006-01-01	17.7876347431375
2007-01-01	17.2719438087779
2008-01-01	16.8925507907746
2009-01-01	17.0886250022705
2010-01-01	17.1900082474317
2011-01-01	16.9272194485257
2012-01-01	17.1937797931653
2013-01-01	17.0792602668545
2014-01-01	17.1950444036109
2015-01-01	16.6348126875561
2016-01-01	16.5607741529849
2017-01-01	16.0751598900196