April 15, 2011

More Quality Indicators from the 2010 Census

In addition to publishing detailed numbers from the 2010 Census, the Census Bureau has been releasing performance indicators from the count. They offer clues to help answer the question of how well the bureau did in counting the entire U.S. population, only once, and in the right place.

The most crucial evidence, an independent post-census quality survey, will not be published until next year. That survey will produce measurements of undercounts and overcounts of specific race and Hispanic groups. However, other information is available now that speaks to the completeness of the count as well as to its data quality. This posting explains some of these key metrics and places them in a chronological narrative of the census-taking process.

Mail Participation Rate: The Census Bureau mailed millions of forms in March 2010. An early important indicator was the mail participation rate: 72% of occupied households sent back their forms, the same as for the short form in 2000. This was a good result, both for cost and quality. Non-response follow-up is expensive, and mailed-in census forms tend to have more accurate information than can be obtained from interviews weeks or months after Census Day, April 1.

Follow-up Counts: The Census Bureau began its non-response follow-up operation May 1. Census-takers made up to six attempts to contact each household from which forms had not been received—about 47 million of them.  If they could not reach the occupants, they would try to get information about them from “proxies, ” secondhand sources such as neighbors or building managers.

Census-takers resorted to secondhand sources to obtain information about more than a fifth of those follow-up households—22%. That was higher than in 2000, when data on 17% of follow-up households came from proxies. This has implications for data quality, because secondhand information is less reliable.

Overall Count Rate: By the time census-takers were done with the follow-up phase of the count, they had obtained at least some usable information from 99.62% of the nation’s housing units, either from census forms or interviews, according to Census Bureau statistics. That was slightly better than the 99.45% total in 2000.

If census-takers could not obtain usable information about a household address—in some cases, they did not even know whether the address was a housing unit—they used statistical methods to fill in the missing data. That procedure is known as imputation, which will be discussed in a later posting.