Year	Percent
1979-01-01	21.5565676814144
1980-01-01	21.6586884211669
1981-01-01	21.9498576544210
1982-01-01	22.5685191367395
1983-01-01	23.2846715945692
1984-01-01	23.7433480989821
1985-01-01	24.2441303528498
1986-01-01	24.1373392645824
1987-01-01	24.6570461043625
1988-01-01	24.7621246201390
1989-01-01	24.5549765636121
1990-01-01	24.4074442754488
1991-01-01	25.3542259534006
1992-01-01	25.8652764574053
1993-01-01	26.4525859132464
1994-01-01	26.3912886073026
1995-01-01	26.1913514198752
1996-01-01	26.4200746827429
1997-01-01	26.9956854052799
1998-01-01	27.3009204492853
1999-01-01	27.7595162897946
2000-01-01	27.9052451681193
2001-01-01	28.1369992071463
2002-01-01	28.2093929464712
2003-01-01	28.4584343597159
2004-01-01	28.4885340716852
2005-01-01	27.9131300972443
2006-01-01	27.7628182193292
2007-01-01	27.4902057420698
2008-01-01	27.3798657376978
2009-01-01	27.6951119351504
2010-01-01	27.6393175929398
2011-01-01	27.8268717250492
2012-01-01	28.2720661605258
2013-01-01	28.6076983070138
2014-01-01	29.0426240874453
2015-01-01	28.9026990405475
2016-01-01	29.3914491675762
2017-01-01	29.3152545975224