Avoid counting an ACS subtotal and its children twice

Read the shell before doing arithmetic

A detailed table may contain a total, subtotals, and increasingly specific categories. Labels alone are ambiguous: the same word can appear under different parents. Record the table ID, line number and complete ancestry of each selected row. Check the table universe separately; “households” and “people in households” are different units.

Choose a single counting rule

For an additive count, select mutually exclusive rows that jointly cover the intended group. Either take the subtotal or add its children. Where detailed data are unavailable, keep the subtotal rather than combining it with only some children. This approach does not apply to medians, averages or percentages without appropriate weights.

Hypothetical shell

A fictional table has 100 households: 60 owners and 40 renters. The renter branch contains 30 with cash rent and 10 without it. “Renter” plus “cash rent” gives 70 on paper, but 30 households are represented twice. The intended numerator for all renters is 40; for renters paying cash it is 30. With all households as denominator the percentages are 40% and 30%, respectively.

Before releasing code, ask someone to reconstruct the selected branches using only the saved shell and line numbers. If they obtain a different group, revise the definition. An arithmetic match to a headline total is useful for checking, but by itself cannot establish that row labels have the same meaning across releases.

Primary source checked 7 November 2026: U.S. Census Bureau: ACS table shells and universes.

Use this in your study: Subtotal double-count screen.