Methodology

PUMSdata turns the U.S. Census Bureau's American Community Survey (ACS) Public Use Microdata Sample (PUMS) into interactive maps, rankings, and custom population estimates. This page explains exactly where the numbers come from, how they are computed, and the limitations you should keep in mind.

1. Data source & vintage

All current figures come from the ACS 2024 1-Year PUMS, published by the U.S. Census Bureau — the most recent complete PUMS release. It covers 51 geographies (the 50 states plus the District of Columbia) and 2,462 Public Use Microdata Areas (PUMAs) — Census-defined sub-state areas of roughly 100,000+ residents each, the most detailed geography PUMS supports.

The release is a sample of 3,422,888 de-identified person records (plus the associated housing records), weighted to represent a total population of 340,110,990 people.

2. Microdata & weighting

Unlike the Census Bureau's published summary tables (which are pre-computed totals), PUMS is record-level microdata: one de-identified row per sampled person or housing unit, each with hundreds of variables. That is what lets PUMSdata answer questions the standard tables don't — arbitrary cross-tabulations like "renters aged 25–34 without a vehicle."

Because PUMS is a sample, every record carries a statistical weight(person weight PWGTP, housing weight WGTP) indicating how many people or households it represents. PUMSdata applies these weights on every query — a population estimate is the sum of the weights of the matching records, not a raw record count. Statistics are computed over the correct universe: for example, the bachelor's-degree rate is taken over adults 25 and older, not the whole population, and medians (income, rent, home value) are weighted medians.

Our medians are true weighted medians of the microdata— the value at the 50th percentile of the weighted records. The Census Bureau's publishedmedian tables instead interpolate within coarse value bands (for example a single "$500,000–$749,999" home-value band), which smooths over the fact that respondents round their answers. Because home values especially pile up at round figures (many owners report exactly "$500,000"), our microdata median home value can read a few percent belowthe Bureau's published figure for the same place; income and rent medians track the published numbers closely. For an exact match to a specific published table, consult the source table on data.census.gov.

3. Sampling error & reliability

PUMS is survey-based, so all estimates are subject to sampling error. National and state figures are precise; individual PUMAs and small subgroups are noisier, and a very small matching population should be read as approximate. Estimates are also subject to non-sampling error (measurement, non-response, and processing), which the Census Bureau works to minimize through extensive quality control.

PUMSdata does not yet display margins of error.Formal margins require the Census Bureau's replicate weights; adding per-estimate confidence intervals is a planned upgrade. Until then, treat small-area and small-subgroup figures as indicative, and consult the Census Bureau ACS methodology for the official reliability guidance.

4. De-identification & privacy

PUMS is de-identified by the Census Bureau and is designed so that individuals cannot be identified; attempting to re-identify any person in the microdata is prohibited. PUMSdata does not collect or hold personal information about the people represented in the Census data. For what we collect about you as a user, see our Privacy Policy.

5. Not affiliated with the Census Bureau

PUMSdata is an independent product and is not affiliated with, endorsed by, or sponsored by the U.S. Census Bureau or any government agency. We repackage public-domain Census data for easier exploration. The underlying data is a work of the U.S. government and is in the public domain.

6. Limitations & appropriate use

Estimates are provided for informational and analytical purposes onlyand should not be the sole basis for financial, legal, lending, housing, employment, or other consequential decisions. For critical applications, confirm against the Census Bureau's official published tables.

7. Historical data & year-over-year

PUMSdata includes prior ACS years (currently 2023and earlier) for year-over-year comparison. Each year uses the same weighting and methodology described here. Dollar figures within a year reflect the Census Bureau's income/housing adjustment factors; cross-year comparisons are nominal unless otherwise noted.

8. References

For per-variable definitions and code values, see the PUMS data dictionary. For the authoritative source material, see the Census Bureau PUMS documentation and the Census Bureau ACS methodology.