Year	Percent of Total
1960-01-01	28.6056661242958
1961-01-01	29.2793916413973
1962-01-01	29.9450193191651
1963-01-01	30.5464382770641
1964-01-01	31.0251041740367
1965-01-01	31.3471672674110
1966-01-01	31.4985481773059
1967-01-01	31.4873425070034
1968-01-01	31.3337999544990
1969-01-01	31.0834048948046
1970-01-01	30.7598547266662
1971-01-01	30.2094198474406
1972-01-01	29.6858069697823
1973-01-01	29.1665145909717
1974-01-01	28.6234751755055
1975-01-01	28.0514746844183
1976-01-01	27.5433815785097
1977-01-01	26.9962883916445
1978-01-01	26.4421094860035
1979-01-01	25.9379131303726
1980-01-01	25.5219898370168
1981-01-01	25.2328692544878
1982-01-01	25.0311767896028
1983-01-01	24.9137510971454
1984-01-01	24.8536589947168
1985-01-01	24.8260893676049
1986-01-01	24.8706146738092
1987-01-01	24.9124310053934
1988-01-01	24.9375709568774
1989-01-01	24.9268173979753
1990-01-01	24.8603053542344
1991-01-01	24.8150083909784
1992-01-01	24.7497492490684
1993-01-01	24.6684781292979
1994-01-01	24.5779585776226
1995-01-01	24.4761567638321
1996-01-01	24.1512093863473
1997-01-01	23.8277792892310
1998-01-01	23.4791777974984
1999-01-01	23.0767232419384
2000-01-01	22.6097979716052
2001-01-01	22.0091041363720
2002-01-01	21.3824574907890
2003-01-01	20.7287617911188
2004-01-01	20.0747618361694
2005-01-01	19.4571682855434
2006-01-01	19.0158994488720
2007-01-01	18.6348588497757
2008-01-01	18.3348101169585
2009-01-01	18.1305064538158
2010-01-01	18.0180312175290
2011-01-01	18.1053380564511
2012-01-01	18.2109340974882
2013-01-01	18.3381241797272
2014-01-01	18.5005758518926
2015-01-01	18.7137924507102
2016-01-01	18.9478537883352
2017-01-01	19.1826507817746