I am using a national telephone survey conducted every year by the CDC called the Behavioral Risk Factor Surveillance System (BRFSS) to answer a question about breast cancer screening rate in low-income counties vs. higher income counties in one state. The number of respondents in one year from the low-income counties is rather low, so I am interested in aggregating the survey data from 2011, 2012, and 2013. The survey methodology did not change substantially in that time.
Here is a CDC document on the BRFSS methodology: http://www.cdc.gov/brfss/data_documentation/PDF/UserguideJune2013.pdf
My question is: are there statistical issues if I aggregate the three years of data to have a larger sample of data? I will need to calculate crude screening proportions but also eventually use logistic regression as well to control for socioeconomic confounders. I appreciate your help!