Year	% of expense
1988	2.254299904582487
1989	3.9419953097097613
1990	11.563422287720718
1991	13.093788063337394
1992	10.666425097037292
1993	10.460867356039763
1994	11.27009195935242
1995	10.635333660968161
1996	14.175108705708206
1997	13.384450990585108
1998	11.301440242784892
1999	12.023507700982726
2000	18.6986442933316
2001	19.217352264267387
2002	18.597506467274037
2003	24.225479619391294
2004	30.61714494498979
2005	30.466728692841805
2006	26.146444833234334
2007	27.247755414643777
2008	28.407512530949937
2009	24.909758004990536
2010	17.77911303520722
2011	25.29156063433826
2012	31.907750096745442
2013	31.736811999408758
2014	32.876386923196094
2015	32.77542161082224
2016	31.58699326810261
2017	31.340154413941075
2018	31.325732931210887
2019	33.39206259300564
2020	31.55418359810081
2021	29.66650222841862
2022	33.18461994235587