Census Accuracy and The Undercount: Why It Matters; How It’s Measured

At a macro level, the 2010 Census appeared to be close to perfect. The Census Bureau reported a net national overcount of 0.01% in 2010, a number not statistically different from zero. Similarly, no state had a statistically significant net undercount, according to Census Bureau estimates. But the apparent precision can be misleading and doesn’t tell the whole story. This Fact Sheet discusses what we know about census accuracy and why it matters to funders and their grantees.

The Census Bureau’s goal is to “count everyone once, only once, and in the right place.” If the census missed relatively equal percentages of people in all communities and demographic groups — urban, suburban, and rural; poor and wealthy; predominantly White and predominantly Black or Latino; young children and senior citizens — the result might not be 100% accurate, but at least it would be fair for key purposes for which census figures are used: allocation of political representation and government funding for vital services and programs.

However, scientific measurements of census accuracy since 1940 have shown a persistent, disproportionate undercount of certain population subgroups, which skews the results in favor of some communities over others.