Year	% of revenue
1990	10.878774222622804
1991	8.13938144329897
1992	9.820549098268174
1993	8.640995305881006
1994	8.360222876965203
1995	7.664199100265192
1996	6.845627553132706
1997	7.7239024706940445
1998	9.408373287926992
1999	8.69998321655355
2000	9.228372138958639
2001	12.07796613995167
2002	12.856854062126935
2014	24.282947368421056
2015	24.35805030680258
2016	24.644145252894766
2017	28.24326434342886
2018	25.112451416931115
2019	28.39044401855299
2020	27.88897568598432
2021	29.532451954939106
2022	23.160412010561828