Year	% of population
1980	37.9
1988	34.9
1989	34.9
1991	34
1992	31.4
1996	35.8
1999	37.8
2000	34.7
2001	37.1
2002	34.7
2003	33
2004	33.5
2005	32.2
2008	33.2
2009	32.6
2010	31.4
2011	30.5
2012	30.4
2013	30.2
2014	29.6
2015	28.9
2016	28.6
2017	28.2
2018	28.4
2019	29.2
2020	30.9
2021	30.5
2022	29.3