Year	% of population
1971	19
1973	17
1975	15.7
1977	15.7
1979	15.5
1981	14.2
1982	14.5
1984	15.2
1985	15
1986	14
1987	13.7
1988	12.7
1989	12.7
1990	13.7
1991	14.2
1992	14
1993	14.2
1994	14
1995	14.5
1996	15
1997	14.7
1998	14.7
1999	15.2
2000	15
2001	14.7
2002	14.7
2003	15.5
2004	15.2
2005	15
2006	14.5
2007	14
2008	15
2009	14.7
2010	14.5
2011	13.7
2012	15.7
2013	16
2014	14.5
2015	15.2
2016	14.5
2017	14.7
2018	13.5
2019	12.5