Year	Percent
1972	12.90268
1973	12.48364
1974	12.63641
1975	12.70294
1976	14.09975
1977	13.96491
1978	14.28632
1979	13.89606
1980	13.77117
1981	12.32283
1982	14.93487
1983	15.59785
1984	13.97016
1985	13.81212
1986	15.59258
1987	16.35546
1988	15.09764
1989	13.0003
1990	15.12129
1995	18.58084
1996	18.63609
1997	19.5219
1998	20.52808
1999	21.43305
2000	22.47052
2001	20.93777
2002	21.26688
2003	19.70768
2004	19.13473
2005	20.32651
2006	19.9792
2007	20.24284
2008	20.21361
2009	19.77568
2010	20.214
2011	22.07373
2012	23.6036
2013	23.73982
2014	24.38143
2015	24.93818
2016	26.69701