Year	Percent
1980	6.556
1981	6.453
1982	6.383
1983	6.32
1984	6.225
1985	6.143
1986	6.077
1987	5.937
1988	5.894
1989	5.908
1990	6.001
1991	6.154
1992	5.611
1993	5.449
1994	5.426
1995	5.329
1996	5.179
1997	5.069
1998	5.024
1999	4.945
2000	4.869
2001	4.842
2002	4.706
2003	4.489
2004	4.296
2005	4.135
2006	4.077
2007	3.998
2008	3.917
2009	3.714
2010	3.666
2011	3.653
2012	3.566
2013	3.47
2014	3.426
2015	3.365
2016	3.329
2017	3.289
2018	3.223
2019	3.145
2020	3.081
2021	3.019
2022	2.957
2023	2.892
2024	2.824