Year	% of revenue
1979	69.8744769874477
1980	71.2280701754386
1981	70.80200501253134
1982	63.60485268630849
1983	57.402812241521914
1984	56.269113149847094
1985	43.19899244332493
1986	57.457212713936435
1987	55.106621773288445
1988	51.46170572602078
1990	46.86921081882179
1991	53.87328378889029
1992	46.014623037276756
1993	47.11140178766078
1994	53.04210802766348
1995	54.555160142348754
1996	54.41994247363375
1997	52.52719481375673
1998	53.181888906177065
1999	56.00324134515824
2000	57.19653789318134
2001	58.23623304070231
2002	59.72181227863046
2003	58.54463468827604
2004	51.60987074030552
2005	62.36702418139322
2006	61.1709011089816
2007	61.443720387009435
2008	54.5898411156969
2009	52.245276092922445
2010	54.889497660674714
2011	47.78112752504883
2014	26.74941340504322
2015	27.293450265409103
2016	26.633788361674902
2017	23.83039005514952
2018	24.2407833166676
2019	23.631898899416996
2020	24.256465277404097
2021	27.3652556297842