Year	Percent
1972	13.42096
1973	14.31319
1974	13.17063
1975	14.72231
1976	16.26579
1977	16.66193
1978	16.51179
1979	14.59271
1980	14.3387
1981	15.26895
1983	13.93807
1984	10.80097
1985	11.34561
1986	11.7282
1987	12.14196
1988	11.02717
1989	11.24919
1990	11.55833
1991	12.49517
1992	12.96883
1993	13.34277
1994	15.20147
1995	13.97677
1996	15.19952
1997	19.05054
1998	14.67895
2008	17.69632
2009	18.26136
2010	19.40537
2011	18.74409
2012	18.39276
2013	18.53189
2014	18.06982
2015	18.23819
2016	18.32477