Before analyzing these data, it is best to have some information about the dataset. First of all, it is useful to know how the data were collected and what sorts of error might be present in the data. The section on survey research listed below attempts to answer those questions by discussing survey research methods in general and the methodology behind the 2004 ANES survey in particular. It also is important to understand the codebook, which describes the dataset. The section on the codebook describes the information contained in the codebook entries for each variable and provides some additional information for some variables.