Year	% of revenue
1972	7.803617571059432
1973	13.134851138353765
1974	9.773712084737603
1975	10.447245726126749
1976	10.137704918032787
1977	10.799925065567628
1978	11.808225562157753
1979	11.625161830782119
1980	11.607317550381529
1981	11.358386302900367
1982	13.191418191278817
1983	14.597935079635494
1984	14.797416821132636
1985	15.543324079677499
1986	15.649252477742316
1987	16.313734317731697
1988	16.68138560364352
1989	16.86390124953504
1990	14.294331587097808
1991	12.946510514858382
1992	14.513473453416712
1993	14.41217121315835
1994	15.075329123010908
1995	15.05891514989551
1996	14.057289850424429
1997	13.995505413638343
1998	13.113956890534748
1999	12.954663938235658
2000	13.011724908616554
2001	15.42758086539785
2002	14.655547436885291
2003	13.037735980837443
2004	12.634940133867149
2005	21.639941317483178
2006	23.539159197126047
2007	24.721122659840173
2008	36.97167145742234
2009	34.24225871198739
2010	25.110982875200357
2011	27.024423483743398
2012	27.264703972094097
2013	25.609331786724184
2014	20.91412916714193
2015	19.744542121271003
2016	14.870031776956194
2017	19.61664243252558
2018	20.435406842419813
2019	17.92599655474951
2020	14.250859848078681
2021	16.085194833629945
2022	18.681027074786307