Year	1=low to 6=high
2005	2.3
2006	2.3
2007	2.3
2008	2.3
2009	2.4
2010	2.4
2011	2.6
2012	2.8
2013	2.9
2014	2.9
2015	3
2016	3.2
2017	3.3
2018	3.4
2019	3.5
2020	3.5
2021	3.6
2022	3.7
2023	3.7