Next week, the U.S. Census Bureau is releasing two important sources for health insurance statistics in the United States: the Annual Social and Economic Supplement to the Current Population Survey and the American Community Survey.

Many people ask us which estimate they should use. Well, it depends. The benefit of the Current Population Survey is the combination of detailed employment and detailed income information, along with the health insurance coverage statistics, which provides an excellent overall picture of the well-being of our nation. With the new Current Population Survey baseline in 2013, annual comparisons are rich with detail. For detailed analysis of subnational geographies, we recommend using the American Community Survey statistics because of its larger sample size and smaller sampling errors. Also, the American Community Survey can provide historic comparisons back to 2008.

Both surveys have questions that attempt to measure the same phenomena. They obtain a person’s health insurance status by asking if they have insurance through a number of different sources, such as an employer, directly through an insurance company, Medicare, Medicaid, Veterans Administration and other public sector insurance, and the military. So, how are the two surveys different? They differ in the timing of data collection, the reference period, the time frame of the resulting health insurance coverage estimates, and, ultimately, in uses of the data.

The Current Population Survey has produced health insurance statistics since 1987, making it one of the most widely used sources of statistics on health insurance coverage in the United States. The survey provides information on health insurance status (insured or not insured) for the nation and by demographic groups. The Current Population Survey is sponsored jointly by the U.S. Census Bureau and the U.S. Bureau of Labor Statistics to provide monthly labor force statistics for the population of the United States. Detailed employment and income data available from this survey make it possible to view changes in health insurance coverage in relation to changes in the overall economic well-being of the nation.

Two years ago, after more than a decade of research, we implemented redesigned health insurance coverage questions in the Current Population Survey to improve the accuracy of our measure of health insurance coverage. With this strong baseline beginning with calendar year 2013, we can measure the impact of the major provisions of the Affordable Care Act that went into effect in 2014, as well as any future changes in health insurance coverage.

Starting in 2008, the Census Bureau also began asking about health insurance coverage using the American Community Survey. With its much larger sample size, we can see health insurance statistics for subnational geographies, such as states, counties, metro areas, congressional districts and cities. This level of geographical detail is not available from any other survey that collects data on health insurance coverage.

The concept of “uninsured” is also slightly different between the two surveys. In the Current Population Survey Annual Social and Economic Supplement, which is conducted in February through April, respondents answer questions about whether they had health insurance coverage at any time in the previous calendar year. The survey, thus, measures if a person was insured on any day during the previous year. Individuals are considered “uninsured” only if, for the entire year, they had no coverage under any type of health insurance.

In contrast, the American Community Survey is a rolling sample of households collected continuously all year long. We ask if a person is currently covered by any of the listed types of health insurance. So, the American Community Survey measures health insurance for the population based on whether people are insured at the point-in-time that they answered the survey during the year of collection.

There is also a variety of differences in the survey logistics. Census Bureau field representatives conduct the Current Population Survey by personal visit or telephone. For the American Community Survey, many respondents receive a paper form to complete and return in the mail or they can reply via the internet. Because of space limits within a paper survey, the American Community Survey asks fewer and less detailed questions than the Current Population Survey. In addition, the American Community Survey asks about the insurance coverage of each household member specifically, while the Current Population Survey asks if anyone in the household is covered, and if so, who that is.

With these variations and others, the two surveys produce consistent, though slightly different statistics on health insurance coverage.