Year	% of population
1988	65.2
1990	58
1992	50
1994	42.5
1996	35.4
1998	38.6
2000	42.3
2002	32.4
2004	26.8
2006	21.9
2007	20
2008	20.4
2009	17.9
2010	16.4
2011	13.2
2012	12.6
2013	10.9
2014	10.5
2015	7.2
2016	8.6
2017	7.9
2018	9.8
2019	6.2
2020	6.8
2021	6.3