Having worked with Census data for more than thirty-five years I consider most of it to be horrifically unreliable. It is also better than IRS data. The best census data is the basic county-level data (believe it or not) since the definitions and methods of counting are fairly stable at that level (particularly from 1960 on).
I would, therefore, suggest that you use county-level data, even if much of it is not electronic. 
Tim H. Blessing, Ph.D.Professor of History and Political ScienceAlvernia University

 		 	   		  
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