How the migration figures are made

What a flow is

A flow is the count of tax filers whose state changed between two filing years. The IRS matches each year’s individual returns to the next year’s, and counts the returns that moved from one state to another. Each is counted two ways: as returns, which stand for households, and as exemptions, the persons those returns claim. Adjusted gross income (AGI) is the year-two return’s, in thousands of dollars, attributed to the destination state.

A state’s inflow is the returns that moved into it from another state. Its outflow is the returns that moved out. The net is the inflow less the outflow: movers from other states, not population change.

The periods

The IRS names each file by its filing-year pair. The pages load the 2021 to 2022 and the 2022 to 2023 pairs, and each is its own period. A change between them is a change between two periods, not a trend, and no page calls it one.

What withheld means

The IRS deletes a state pair with fewer than ten returns. The publisher’s own words, from the users guide: “For the state-to-state migration flows a cell must have at least 10 returns to be shown.” The file writes a deleted cell as −1, and this site carries it as withheld, with the reason the IRS gives.

This site adds its own cut, which is the site’s choice and not the IRS’s: a count of 1 to 10 returns or persons is withheld too, as the rest of the site does. A pair of 11 or more is withheld as well where that is needed so that a total cannot give a withheld pair back (see below). Such a pair gives the same reason as a cut, so a reader cannot tell the two apart. A withheld figure has no value. It is never printed as zero, and no page infers it from another figure.

Why a total can be withheld

A withheld pair is held back from the totals it adds to, so that a total cannot give it back. Each pair sits in two totals: its destination’s inflow and its origin’s outflow. A total that holds a withheld pair prints only where it holds at least two withheld pairs whose counts add to 11 or more; a deleted count is not known, and adds nothing. Where it does not, the smallest shown pair in that total is withheld as well, and that pair’s other total is checked in turn, until every total is held. A total with no shown pair left to withhold is dropped, and so is the net that uses it. The state then prints as withheld for that measure.

No total is summed from pairs on any page, and no national total is printed. A national sum of the pairs would give back the cells the state totals withhold.

State totals are not county sums

The IRS’s state total is the state file’s own “Total Migration-US” row, and it is not the sum of the county flows. The IRS says “records may be removed at the county level that are not removed at the state level”. The county pages are not yet built, and this page prints the state file’s totals only.

What the data cannot show

Movers, not migrants, and not people who left for good. No causes: the files do not record why anyone moved, and no page says they did. Filers, not the whole population, because many individuals are not required to file. The IRS counts returns and exemptions, not households or residents. Years are not one another’s trend.

The source

IRS Statistics of Income, state-to-state migration flows, from the IRS Statistics of Income migration data page. The IRS states no license; the files are a U.S. Government work in the public domain (17 U.S.C. 105).

What this data cannot show

• Movers, not migrants: a flow is a count of tax returns, or of the exemptions they claim, whose state changed between two filing years. It does not show who left for good, who came back, or how many people lived in each state.
• Net is not population change. Births, deaths and movers from abroad are not in a state’s net, and the file records where filers were, not why they moved.
• Filers, not the population: many individuals are not required to file, and the file covers the returns that were filed and matched.
• Counts of 1 to 10 returns or persons are withheld, and so are the cells the IRS deletes, and a pair of 11 or more is withheld where a total would otherwise give a withheld pair back. A state whose total is dropped has no net, and a withheld figure is never a zero.
• A state’s total in the state file is not the sum of its county flows; the pages print the state file’s totals only, and the methodology says why.

Sources

• Statistics of Income: state-to-state migration flows (county flows are not yet loaded) — Internal Revenue Service, Statistics of Income · Public domain — U.S. Government work · Updated: Annual, by filing-year pair; the IRS updates each year page