Year	% of population
2002	20.7
2003	19.9
2004	19.6
2005	20.5
2006	20.3
2007	20.1
2008	19.7
2009	20.1
2010	21.4
2011	23.1
2012	23.1
2013	22.1
2014	21.4
2015	21.2
2016	20.2
2017	18.5
2018	17.9
2019	17.7
2020	19.6
2021	18.8