The U.S. Census Bureau had a last-resort solution for getting information on households that failed to respond to the once-a-decade head count. It’s called “imputation,” and it involves using information about neighbors with similar characteristics to fill in information gaps about households with missing data. The statistical technique is used often in hard-to-count places, where racial and ethnic minorities are more likely to live, and where people could otherwise go uncounted. Fewer than 1% of households were counted this way for the 2020 census. Conservative groups are raising questions, suggesting it may be grounds for legal challenges of the data used for drawing congressional and legislative districts.