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I want to combine the 2005 and 2006 ACS microdata. What do I do to the weights?
Multiply the weight by 0.5. Assuming you are using the concatenated version of the ACS data and have selected the data for years 2005 and 2006:
nwgt = perwt * 0.5;You need to be careful when you combine the two years. The group quarters population was not in the 2005 sample and is in the 2006 sample. Thus, the group quarters population should be excluded from all your tabulations.
The following is a link from the Census Bureau , which provides information on comparing ACS data (between the census and ACS and/or across ACS years):