Year	% of expense
1972	3.59509819696836
1973	3.8461538461538463
1974	3.7943135892572863
1975	4.431279620853081
1976	4.466383812010443
1977	5.354538730251814
1978	5.880019528866102
1979	6.7691591478418935
1980	7.27821566325675
1981	7.671492355567581
1982	7.097208228408684
1983	7.228996550827047
1984	8.838865891770393
1985	9.505309505309505
1986	10.507337033286179
1987	11.132058028717916
1988	11.27878158755501
1989	10.594040556231963
1990	11.125340827625601
1991	10.047082839457396
1992	10.014237046829715
1993	9.330362993054676
1994	9.89250770702517
1995	9.11283702721475
1996	8.763089005235603
1997	9.651277441540929
1998	9.312991997918157
1999	7.847983644917897
2000	7.570082099627758
2001	7.090801820193963
2002	6.122877264769336
2003	5.7582656664441
2004	5.58448993428754
2005	5.44613612980565
2006	5.43606953230751
2007	5.567449349328833
2008	5.527432643883141
2009	4.7644626997497
2010	4.982028935686048
2011	5.782613179067707
2012	5.867861282130489
2013	5.5890909444696995
2014	5.54168720559016
2015	5.27986064633929
2016	4.764323946506805
2017	4.359302594712098
2018	4.05233082977475
2019	3.8027367932457943
2020	3.453646014585906
2021	2.8311745865759455
2022	3.3910194430172544