Year	% of expense
1997	23.252518891687657
1998	22.03120557132734
2002	25.29284704452421
2003	26.94358047764529
2004	25.49610848543041
2005	28.196494288027164
2006	27.698725777303412
2007	26.36517230101012
2008	27.07379143802782
2009	27.682186208570513
2010	35.977748502436775
2011	34.40081337164888
2012	35.5887568364776
2013	36.67058069857047
2014	32.62346772357212
2015	31.769534868916814
2016	34.10061451932091
2017	33.48432753303338
2018	39.1716458250881
2019	36.1846741049808
2020	36.00294185956491
2021	34.12039334284496