Year	% of population
1981	38.9
1988	36.9
1990	35.2
1992	33.5
1994	29.4
1996	27.4
1998	27.9
1999	28.7
2000	29.5
2002	27.2
2004	26.2
2006	25.4
2007	24
2008	24.1
2009	23.5
2010	21.8
2011	19.3
2012	21.5
2013	19.7
2014	19.5
2015	18
2016	18.6
2017	18.7
2018	18.9
2019	16.9
2020	18
2021	17.1