Year	% of expense
1988	43.02624406198895
1989	41.38425443169969
1990	38.25301204819277
1991	36.53009239677034
1992	26.710125659390144
1993	42.06265052642367
1994	33.452293106404454
1995	36.44498970391542
1996	38.05814840429127
1997	40.87085675523718
1998	38.14970841076116
1999	34.690125095625795
2000	37.165085751805435
2001	37.85680728189016
2002	40.04173096305236
2003	34.899757232280606
2004	33.71701570284724
2005	32.826057248828675
2006	35.037433840699414
2007	34.10176007041172
2008	35.96134945178442
2009	32.62840801681136
2010	38.38875669301625
2011	39.88579964538062
2012	40.76716202540592
2013	43.64561152154798
2014	40.09380300787574
2015	39.438872512173
2016	38.809683031614
2017	38.255476561819634
2018	37.170856397858124
2019	35.99906124505026
2020	38.00681904840172