As of dates in statistics and official data

Reference period and release date

The reference period is the time a statistic measures. The release date is the day an agency publishes it. The two are always apart, and the gap matters when you place a number on a timeline.

The US Bureau of Labor Statistics shows this in its monthly Employment Situation report. Its technical note says the household survey reference period is the calendar week that contains the 12th day of the month, in general ¹. The establishment survey uses the pay period including the 12th, which may not match a calendar week ¹. A jobs figure for a month describes one week or pay period in that month, not the whole month.

Vintages and revisions

A number published today may change next month. Each published version is sometimes called a vintage. When you cite a figure, say which release it came from.

BLS says the prior two months of establishment survey estimates are routinely revised to add more sample reports and updated seasonal factors ¹. It says an estimate is final only after two successive revisions, and that the survey estimates are adjusted once a year to payroll counts from unemployment insurance records ¹.

The UK Office for National Statistics separates two kinds of change. Its policy, last updated on 9 August 2024, defines revisions as updates to previously published statistics, analysis or data that improve quality ². It defines corrections of errors as amendments made in response to the identification of mistakes ². It says revisions can add data not available at first publication or follow new or improved methods, and are usually reported in the next release ².

As of labels on legal and regulatory texts

Official databases of law and rules carry as of dates too. These tell you how current the text is, not when the law was made.

How to record an as of date

• Write the reference period, for example the week or month the number describes ¹.
• Write the release or publication date of the version you used.
• Note whether the number can still be revised under the agency's policy ^1,2.
• For legal texts, copy the as of, current to or amended up to date shown by the database ^3,45.
• Store dates in ISO 8601 form so they sort correctly.

Common mistakes

Three errors recur. The first is dating a statistic by its release date as if the event happened then. The second is quoting a first estimate after it has been revised, without saying so ^1,2. The third is quoting a consolidated law as if it were the text in force on an earlier date. eCFR notes that it is an unofficial, continuously updated version and that the official edition may differ ³.