Year	% of expense
1990	56.40721404841006
1991	61.08007448789572
1992	59.63480128893662
1993	55.29043614316448
1994	54.63488460083239
1995	64.04822088275326
1996	66.77122132915115
1997	66.77104439123227
1998	68.29531165798454
1999	64.87568830302018
2000	58.4488351518726
2001	58.87119704293432
2002	53.695288208562545
2003	59.776729197836346
2004	56.15537224600605
2005	54.33889663796835
2006	53.149759136066066
2007	54.30596763833236
2008	50.299141483078415
2009	46.92543723268817
2010	44.22418922939601
2011	41.27293339018491
2012	47.93973277419723
2013	45.50751681037228
2014	44.86875449331655
2015	46.150568044242554
2016	45.785153591665114
2017	45.160542697762665
2018	43.28919515292912
2019	42.28320602822527
2020	39.50443092083025