Year	Percent
1968-01-01	43.8255034717863
1969-01-01	44.3848940530467
1970-01-01	44.7949136595949
1971-01-01	46.1096012870381
1972-01-01	46.4028208087629
1973-01-01	45.5416235218827
1974-01-01	46.8311453747913
1975-01-01	47.4947050638760
1976-01-01	46.9564028880806
1977-01-01	45.5520364462756
1978-01-01	44.3392379954686
1979-01-01	43.5681140712090
1980-01-01	43.1354693562818
1981-01-01	42.6335149165735
1982-01-01	41.6760649764410
1983-01-01	40.2098942496240
1984-01-01	39.6770608641863
1985-01-01	39.2535016366922
1986-01-01	38.7930752784890
1987-01-01	38.2544427253780
1988-01-01	37.4461009813172
1989-01-01	36.3743088487204
1990-01-01	35.4371245672921
1991-01-01	34.6377060010703
1992-01-01	34.4004638038975
1993-01-01	34.7396399439802
1994-01-01	34.6683933979891
1995-01-01	34.7081846667950
1996-01-01	34.1801555703596
1997-01-01	33.2518659401190
1998-01-01	33.3024577017991
1999-01-01	33.4596608988932
2000-01-01	33.4228374021560
2001-01-01	32.6750076957244
2002-01-01	32.5757610832939
2003-01-01	32.1795766605424
2004-01-01	31.8221524805926
2005-01-01	31.1538703691437
2006-01-01	30.5908960154156
2007-01-01	29.8327458519023
2008-01-01	29.4743447001787
2009-01-01	28.6324008025329
2010-01-01	28.2613332865610
2011-01-01	27.7726697534283
2012-01-01	27.7681363371741
2013-01-01	26.2552806746283
2014-01-01	25.3375765311732
2015-01-01	24.6650177245278
2016-01-01	23.6526776823060
2017-01-01	22.4976497568840