Year	% of expense
1972	2.932551319648094
1973	3.36
1974	3.323689224472514
1975	3.0627148341710075
1976	4.220538656476237
1977	5.100368993175763
1978	5.628419795196658
1979	6.677124197700573
1980	7.223062779017596
1981	7.415432502546306
1982	6.787010768634222
1983	7.048074614634306
1984	7.792862834272716
1985	9.288663416348214
1986	10.507337033286179
1987	11.132058028717916
1988	10.520623140262458
1989	9.23702433136395
1990	9.46361789470114
1991	8.881825649083984
1992	9.021868113239567
1993	8.413530207879669
1994	9.251737800386813
1995	8.22985231701899
1996	8.446334385779206
1997	9.277101970209092
1998	8.98609293648197
1999	7.7650411242795165
2000	7.592584772602508
2001	6.812543360515922
2002	6.037266550308775
2003	5.51946401520928
2004	5.365659233141839
2005	5.1513422026293
2006	4.741097357330825
2007	4.498248840448405
2008	4.531077087829621
2009	4.105866195584156
2010	4.3659628859810535
2011	4.777650497166328
2012	4.870596807905452
2013	4.903803566430915
2014	5.0039956185322385
2015	5.228997361841992
2016	4.727756123400896
2017	4.192192083358998
2018	3.8514113957997558
2019	3.600279667732018
2020	2.962025232005017
2021	2.724053326004487
2022	3.0694809203500752