Year	% of expense
1972	2.2092010452134017
1973	2.022046392101173
1974	1.314724919093853
1975	0.9817095931317658
1976	0.9154929577464804
1977	1.2421130068188893
1978	1.579459348761002
1979	2.1523767214571268
1980	2.3592429941511224
1981	2.6775937585546146
1982	3.114196903233303
1983	3.820202172222649
1984	4.401519211501284
1985	4.7145912498183185
1986	4.326603483314664
1987	4.115358007609831
1988	4.10829441850123
1989	3.579727987295389
1990	3.1043744951369
1991	3.251082007756735
1992	4.234078475711473
1993	8.413530207879669
1994	10.147511826616293
1995	7.518153743427093
1996	8.763089005235603
1997	9.837276450970297
1998	8.886334497546311
1999	7.7650411242795165
2000	7.7340423232388735
2001	7.384922449997921
2002	5.785042877607488
2003	5.13653359519583
2004	4.766846925584021
2005	4.367920729679102
2006	3.9903489235337783
2007	3.832233340430062
2008	3.6420010180943123
2009	3.243126529437167
2010	3.3441805719033444
2011	3.424968003412969
2012	3.463004168904576
2013	3.0569391542142785
2014	2.9701318204572
2015	2.7840516787398624
2016	2.649152758905032
2017	2.5127678925398196
2018	2.3346882693078377
2019	2.164609424272457
2020	1.6029982381277306
2021	1.1824966485924089
2022	1.288373145933603