Period	Percent
1970-01-01	2.00
1975-01-01	2.56
1980-01-01	3.40
1985-01-01	3.27
1990-01-01	3.04
1995-01-01	8.55
2000-01-01	17.02
2005-01-01	17.62
2010-01-01	36.97