further explore differences among the surveys. The focus here is on providing an overview for analysts who may not be familiar with the ACS, the CPS ASEC, or the NHIS estimates of health insurance coverage.

The ACS is a nationwide survey designed to collect and produce economic, social, demographic, and housing estimates on an annual basis. It is conducted in all U.S. counties and Puerto Rico municipios and participation is required by law. About 3 million housing unit addresses are sampled annually throughout the United States and Puerto Rico. There are separate housing unit (HU) and group quarters (GQ) samples. GQ include nursing homes, correctional facilities, military barracks, and college/university housing, among others.

The sample coverage of the ACS is different from other surveys that gather information about health insurance coverage. For example, neither the CPS ASEC nor the NHIS samples institutional GQ, residents of Puerto Rico, or active-duty military members. Furthermore, neither the CPS ASEC nor the NHIS uses a sample that draws from every county equivalent across the United States.

ACS data are collected continuously using independent monthly samples. The ACS uses three modes of data collection for HUs. All sampled households are mailed a paper survey. All mail nonrespondents are followed up with an attempt for a telephone interview, and a sample of roughly one in three telephone nonrespondents is followed up with personal visits. The nonresponse interviews are conducted using computer-assisted instruments—computer-assisted telephone interviewing (CATI) or computer-assisted personal interviewing (CAPI).¹

Respondents living in GQ facilities complete their forms using a different procedure based on the size of the facility. Some respondents fill out the paper form, and some forms are completed by field representatives.

The application of sequential modes in tandem with mandated responses leads to a high unit response rate. The official response rate is derived by estimating the number of completed interviews over the estimated number of units that should have been interviewed. This procedure omits units that are ineligible for the survey (such as businesses) and those that did not respond to the mail or phone interview but were not sampled for personal visit follow-up. In 2008, the response rate was 98 percent.² This approach to calculating the response rate has appealing