Tax Burden is calculated as the ratio of total state and local tax revenues collected in (fiscal year) t to total personal income in (calendar) year t-1. 
 

Personal Income for States, 1958–98: 

US Department of Commerce, Economics and Statistics Administration, Bureau of Economic Analysis, Regional Economic Economic Information System, State Annual Summary Tables 1969-98, Table SA1. http://www.bea.doc.gov/bea/regional/spi/recent.htm 

State and Local Tax Collections: 

1961-1976: U.S. Census Bureau, Governmental Finances, various years. 
1977-1994: U.S. Census Bureau. 
1995-1996: U.S. Census Bureau, State and Local Government Finance Estimates by State. http://www.census.gov/govs/www/estimate.html