Scope and period mismatches between official records

Coverage: who or what is counted

The clearest example is the monthly US jobs report. It draws on two surveys. The Bureau of Labor Statistics (BLS) says the household survey includes agricultural workers, self-employed workers and unpaid family workers, and these groups are excluded from the establishment survey ¹.

Definitions of the event matter too. The National Center for Health Statistics (NCHS) said some local and state health departments reported only laboratory-confirmed COVID-19 deaths, so their counts could differ from death certificate counts ².

Counting unit: people, jobs or records

The same population can produce two totals if one record counts people and another counts positions. BLS says in the household survey individuals are counted only once, even if they hold more than one job ¹. In the establishment survey, multiple jobholders are counted separately for each appearance on a payroll ¹.

Period: reference weeks, quarters and fiscal years

Two records labelled with the same month can cover different days. BLS says the household survey refers to the calendar week containing the 12th of the month, and the establishment survey to the pay period including the 12th ¹.

Years differ across systems. India's quarterly GDP calendar puts April to June in the first quarter and January to March in the fourth ³. Australia's national accounts revise by financial year, and the ABS rolls the chain volume reference year forward each September ⁴.

Geography: where the event is recorded

NCHS said provisional death counts were tabulated by the jurisdiction where the death occurred, not the decedent's state of residence ².

Adjustment: seasonal and base-year changes

Statistics Denmark says adding a new period automatically revises earlier seasonally adjusted figures, even when the unadjusted figures stay the same ⁵. The ABS says rolling the chain volume reference year forward changes levels across the series but not percentage movements ⁴.