Year	% of revenue
1975	6.353467561521253
1976	8.209570957095709
1977	8.39139654650106
1978	13.552143991529912
1979	14.347925739170295
1981	18.763461294818192
1982	17.606406318560772
1983	18.153817435131604
1984	13.672496025437203
1985	14.933937334843336
1986	15.99184961219929
1987	14.213381555153706
1988	14.265892389125852
1989	15.191516019330589
1990	18.05845067426724
1991	17.853261626772927
1992	20.488155061019384
1993	19.38702531093551
1994	17.809824780047773
1995	16.62601737414705
1996	20.244882285174135
1997	20.681296249043125
2002	20.421692389347378
2003	19.115313712362312
2004	22.00656647548059
2005	23.75135979344681
2006	27.436190675403456
2007	28.462723420725816
2008	26.94871200926041
2009	27.81362049402415
2010	25.255097331877707
2011	29.665721329035442
2012	26.154816332965474
2013	29.175224273295065
2014	23.289037824512747
2015	24.112753283467594