Year	% of population
2001	18
2002	19.8
2003	20.5
2004	20.7
2005	21.5
2006	20.5
2007	18.4
2008	15.4
2009	14
2010	13.1
2011	12.9
2012	13.6
2013	14.4
2014	15.4
2015	15.9
2016	16.7
2017	17.6
2018	17.8
2019	18.3
2020	18.7
2021	19.6