Year	% of population
1977	17.2
1978	14.2
1979	15.5
1980	13.7
1981	13.2
1982	13.2
1983	13.5
1984	13.7
1986	14.5
1987	17
1989	14.2
1991	14
1993	19.2
1995	18.2
1998	18.2
2000	17.2
2002	17.2
2003	15.4
2004	15
2005	15.7
2006	15.3
2007	14.9
2008	15.2
2009	15.3
2010	15.9
2011	16.5
2012	16.2
2013	16.4
2014	17
2015	17.8
2016	17.5
2017	17.8
2018	17.1
2019	16.5
2020	17.3
2021	16.6