Year	Percent (Units)
1980	1.108
1981	1.143
1982	1.134
1983	1.087
1984	1.094
1985	1.044
1986	1.009
1987	0.993
1988	0.989
1989	0.977
1990	0.936
1991	0.905
1992	0.797
1993	0.791
1994	0.793
1995	0.789
1996	0.792
1997	0.781
1998	0.764
1999	0.756
2000	0.752
2001	0.753
2002	0.760
2003	0.752
2004	0.747
2005	0.751
2006	0.754
2007	0.754
2008	0.756
2009	0.748
2010	0.732
2011	0.727
2012	0.692
2013	0.690
2014	0.675
2015	0.677
2016	0.663
2017	0.644
2018	0.632
2019	0.616
2020	0.597
2021	0.587
2022	0.579
2023	0.565
2024	0.553
2025	0.542
2026	0.533
2027	0.524
2028	0.515
2029	0.507