Year	% of expense
1973	3.603076923076923
1974	3.323689224472514
1975	3.894872161351832
1976	4.462793424031787
1977	5.207100591715976
1978	5.79146376015587
1979	6.677124197700573
1980	7.223062779017596
1981	7.415432502546306
1982	6.787010768634222
1983	7.048074614634306
1984	7.959505897650228
1985	9.288663416348214
1986	10.381665961647178
1987	10.042642282007904
1988	10.503759302929314
1989	9.20073957835848
1990	9.70687216262785
1991	8.881825649083984
1992	9.021868113239567
1993	8.256414050780355
1994	9.259436215957935
1995	7.747659751309497
1996	7.150055465901214
1997	9.091904352083594
1998	8.886334497546311
1999	7.751632699944209
2000	7.5079701019353395
2001	7.186494869622873
2002	6.197470408330026
2003	5.748739367071323
2004	5.377174013230195
2005	5.1513422026293
2006	4.741097357330825
2007	4.525777082511798
2008	4.531077087829621
2009	4.545520052046229
2010	4.614796355629392
2011	5.004710490749633
2012	5.73045353679712
2013	5.315367098784485
2014	5.315461923956858
2015	4.928273334269164
2016	4.613348983291821
2017	4.192192083358998
2018	4.037418464096025
2019	3.667163292421539
2020	3.0104884363891693
2021	2.802142325694618
2022	3.0694809203500752