Year	% of expense
1998	63.245621392462006
1999	65.37166263080246
2000	62.62527540816903
2001	50.27469606209903
2002	43.20968371729793
2003	47.977885159549
2004	41.53760445682451
2005	39.24904469180927
2006	36.518989097567065
2007	39.91587019973674
2008	36.94010703027637
2009	36.00843844767723
2010	38.26329022988506
2011	37.54104841328779
2012	41.31191040711325
2013	41.96756970535891
2014	42.767151389599164
2015	43.759831519288134
2016	43.61496448390794
2017	40.996055034223296
2018	40.96235740262969
2019	41.01057755874752
2020	34.615930207816156
2021	39.089137562865375