Using the CHAS data for demonstrating local housing needs

[Suzanne_78]

I am attempting to determine the number of households by income group (0 to 30%, etc) in Texas using the CHAS 2009 data. When I use a filter on Household_Income to exclude ALL I can no longer select T in the line type. Then I am left with only 117 counties, out of Texas' 254. As I move forward with my data analysis more clarification on the difference between Line type (T, D, S) would be helpful. The data dictionary lists T=total, D=Data, and S=subtotal. But what do these terms actually mean, when is it appropriate to select T versus D, or S?