Year	% of expense
1998	25.44855137581235
1999	24.6895719285884
2000	28.255818311284337
2001	28.56757780578762
2002	34.345523961837856
2003	30.970682378952414
2004	28.215429243301987
2005	32.826057248828675
2006	33.03829172839611
2007	34.10176007041172
2008	31.316669091185645
2009	30.830101403605088
2010	29.5808791492296
2011	33.37190753485541
2012	29.26216166907192
2013	29.098604001661574
2014	28.270806016525256
2015	28.69934095657497
2016	32.260551385489435
2017	30.87630632976362
2018	32.87432672566302
2019	32.0555334169177
2020	32.37216651712279
2021	31.609661908305164