Year	%
1977	16.1
1983	16.4
1987	16.1
1993	16.2
2004	15.5
2009	15.3
2011	15.3
2015	15.3
2016	15.4
2017	14.9
2018	15.4
2019	16.2
2020	16.1
2021	16.3