What’s the Difference Between 1-Year and 5-Year American Community Survey (ACS) Data?

The American Community Survey (ACS) is an ongoing survey that provides data every year about the social, economic, housing, and demographic characteristics of America’s communities. Results give Illinois communities the current information they need to plan investments and services, such as those that support young children and their families. This is one of several reasons why demographic data from the ACS are an important part of IECAM’s early childhood data collection.

The infographic below summarizes some of the important differences between 1-year (including 1-year supplemental estimates for areas with populations of 20,000 and more) and 5-year estimates.

The differences between 1-year and 5-year estimates are especially important to note when using data to communicate stories or visualize trends. First, for areas with both estimates available, it is important to be consistent in using the same estimate (1-year or 5-year, not a mix). Second, as the chart below shows, actual estimates can vary quite a bit between 1-year and 5-year estimates. In these situations, it is important to consider your overall communication goal. Is it to communicate the variabilities between points of time (sudden changes that can occur due to economic, social, or health events) or a general trend? If it is to communicate sudden changes, then 1-year estimates might be best because they are based on the most current data. General trends, however, might be best communicated using more reliable 5-year estimates.

Margins of error allow data users to measure the range of uncertainty around a given estimate. The ACS sets this range at a standard of a 90% confidence level. In other words, looking at 5-year estimates (in orange) on the chart below, we can be 90% confident that the true percent of children under 6 with public health insurance in Cook County in 2019 lies within the range indicated (44.9–46.5%).

In addition, note that the margin of error is narrower for the 5-year data trend line (in orange), meaning one could have more confidence that the 5-year estimates reflect the result of a survey of the entire population. In general, the larger the sample size, the smaller the margin of error.

Why do margins of error matter? The margin of error can allow you to see if there’s enough evidence to conclude the estimates are statistically different from one another. In short, adding it to a chart can communicate the accuracy of the data.