Guide

Ryszard Cieplechowicz: how to read ACS five-year estimates

Notes Ryszard Cieplechowicz wrote while building the Tampa Bay tables, for anyone loading small-area Census data for the first time.

A five-year estimate covers a period

The 2020-2024 release pools five years of survey responses. It describes that period, not one month and not today. For rents and values, that is different from a current listing.

Every estimate has a margin of error

Small areas have wide margins. Two ZCTAs that differ by a point or two may not differ at all. The tables flag areas with fewer than 300 units because small counts are noisy.

Do not average medians

A median of ZCTA medians is not the median of the area. Sum counts when you can, and say what you summed.

Say what the number is not

Each study here states what it does not measure: not asking rents, not sale prices, not an address-level census. That sentence takes ten seconds to write and prevents most misuse.

Related: ZCTA versus ZIP code and the data hub.