Year	%
1977	3.5
1983	3.6
1987	3.9
1993	3.8
2004	3.7
2009	3.6
2011	3.5
2015	3.6
2016	3.5
2017	3.5
2018	3.4
2019	3.2
2020	3.2
2021	3.3