Year	Percent
1972	16.09744
1973	16.61011
1974	17.05781
1975	19.96152
1976	19.64152
1977	22.03984
1978	22.86777
1979	21.13709
1980	21.57554
1981	22.01996
1982	22.15287
1983	24.58563
1984	24.04653
1985	24.01885
1986	23.33811
1987	23.53081
1988	22.75881
1989	21.82813
1990	22.09734
1991	20.8723
1992	21.4304
1993	22.94553
1994	24.1761
1995	23.70617
1996	23.76687
1997	25.07889
1998	25.57444
1999	24.75653
2000	25.42283
2001	25.15273
2002	24.76226
2003	24.7117
2004	24.23609
2005	25.59576
2006	24.23872
2007	24.65649
2008	24.68836
2009	25.13893
2010	25.01762
2011	24.59235
2012	25.71065
2013	25.89443
2014	25.57325
2015	25.01585
2016	25.73512