The Currency Times

A series that looks clean is usually a series whose faults have not been looked for. Six recur, and all six are silent.

The six silent faults

Fault

What it does

Control

Look-ahead

Uses a figure before it was released, or a revision that did not exist yet.

Release timestamps, reads refused before them

Survivorship

Measures only the cases that lasted, so the failures vanish from the record.

Exits recorded with an outcome rather than dropped from the sample

Identifier drift

Labels get reused and reassigned, so a long join silently changes subject.

Permanent identifiers with date-ranged validity, never a reusable label

Universe drift

Studies the population as it stands today rather than as it stood then.

Membership lists as at the date, point in time

Reporting lag

Treats the period a figure describes as the moment it became available.

Publication date plus a buffer

Definitional break

The series changes what it measures without changing its name.

Break calendar, flagged automatically when a test spans one

The break calendar

Any test spanning one of these dates is testing two different series and calling them one. The engine raises a flag rather than allowing it silently.

Date

What changed

1948, 1968, 1979, 1994, 2013, 2022

Successive revisions of the International Classification of Diseases, each redefining cause of death

1983

Owners' equivalent rent enters the consumer price index

1996

Chain-weighted gross domestic product replaces fixed weight

1998

A national currency is redenominated, and a long-standing correlation between two asset classes reverses

1999

Geometric mean introduced in consumer price index construction

2003

Industry classification moves to NAICS

2005

A second redenomination, six zeroes removed, rescaling every historical value

2013

Research and development capitalised in national accounts

January 2015

Swiss franc peg abandoned

August 2015

Chinese yuan regime shift

2016 and 2018

Sector classification revisions

2019

Lease accounting under ASC 842

1990s onward

Weather station relocation and automation, breaking long temperature records

2020

Case definitions for a novel pathogen revised repeatedly inside a single year

2022

The long-standing correlation between two major asset classes reverses

The same calendar, as a shape

Seventeen breaks in seventy-eight years, and they do not thin out with time. Any test spanning one of these marks is testing two different series and calling them one.

This is the argument for the break calendar in one picture. Not that breaks happen, which everyone concedes, but that they happen constantly, so a long sample is more exposed than a short one rather than less.

Time

Everything is stored in coordinated universal time to microsecond precision and converted only at the point of display. Where two venues disagree on a closing price, one is designated authoritative and the choice is recorded rather than assumed.

Daylight saving is handled by timezone-aware conversion rather than a fixed offset. The transitions in the United States and the United Kingdom do not coincide, which produces two or three weeks in March and about a week in October where a fixed offset is simply wrong.

Under active resolution

One contamination issue in a derived label set is being worked through, and dependent validation is held until it clears rather than proceeding on an unverified base. Holding it is the control working as designed. It is listed under Data integrity in the theories index as open.

Raw deliveries are immutable. Every derived layer can be rebuilt from them. If that is not true, no result is reproducible and the rest of this is decoration.