Year	% of population
1985	29.3
1986	29.4
1987	29.6
1988	29.4
1989	29.5
1990	28.8
1991	29.3
1992	28.6
1993	28.3
1994	28
1995	27.9
1996	27.2
1997	26.8
1998	26
1999	25.7
2000	25.3
2001	25.2
2003	25.2
2004	24.4
2005	24.1
2006	24.1
2007	23.9
2008	23.5
2009	22.9
2010	22
2011	21.2
2012	20.6
2013	20.5
2014	21
2015	21.4
2016	22
2017	22.4
2018	22.5