N06 · Measurement primer
The Revised Past
Can this published value change after its first release?
The number in last year's screenshot may no longer match the table. That can be an error. It can also be the ordinary result of a published revision policy.
01
Separate adjusted and unadjusted
CPI publishes both. Seasonal adjustment removes estimated recurring seasonal influences so shorter-term nonseasonal movement is easier to inspect. Unadjusted data remain important for actual-price comparisons and escalation uses.
02
Read the revision window
BLS recalculates seasonal factors each year and can revise the preceding five years of seasonally adjusted CPI data. Older seasonally adjusted indexes are treated as final. Record the vintage when the difference matters.
03
Preserve what the reader saw
A reproducible claim needs the release date, table, adjustment status, and later correction or revision. Do not silently replace the old observation and pretend the history never moved.
Try to disprove yourself
The strongest honest countercase
Revision is not evidence of manipulation. A method that incorporates later information may be more accurate, provided the revision policy and vintage remain visible.
A question to carry
Where have you seen this number travel too far?
Find a monthly change in a current release and an archived release. Record whether each is seasonally adjusted and whether the value is still revisable.
Transfer test
The revised month
A screenshot shows a seasonally adjusted monthly CPI change that differs from today's historical table.
Is one of them necessarily wrong?
Open the field note
No. Record the release vintage and check the published revision window. The earlier screenshot may be an accurate record of the first release while the current table contains a later revision.
Direct sources
Inspect the method at BLS
- BLS seasonal adjustment in CPI
- BLS seasonal-adjustment questions and answers
- BLS using adjusted and unadjusted data
Sources reviewed August 30, 2026. These links establish the bounded methodological statements used above. They do not make BLS responsible for bent.WTF’s instructional framing.