Year	Percent
1980	3.762
1981	3.67
1982	3.733
1983	3.793
1984	3.717
1985	3.739
1986	3.725
1987	3.777
1988	3.822
1989	3.782
1990	3.66
1991	3.536
1992	3.188
1993	3.205
1994	3.234
1995	3.196
1996	3.158
1997	3.163
1998	3.184
1999	3.176
2000	3.135
2001	3.148
2002	3.136
2003	3.114
2004	3.028
2005	2.981
2006	2.901
2007	2.822
2008	2.733
2009	2.628
2010	2.538
2011	2.478
2012	2.437
2013	2.406
2014	2.393
2015	2.371
2016	2.337
2017	2.294
2018	2.247
2019	2.202
2020	2.156
2021	2.114
2022	2.073
2023	2.033
2024	1.994