Understanding the AUCN Check-Record Index

An index can summarise several measurements, but the name and unit matter. AUCN previously called this series a used-car risk index. The more accurate description is an experimental index of historical check-record flags.

It combines finance-related, written-off and stolen-related flags in AUCN's selected check records. It does not measure Australian fleet risk, expected financial loss or the likelihood that a particular purchase will go wrong.

The historical observation

The unit is index points. A value of 97.2 means the weighted measure was 2.8% below the selected 2023 reference value under this formula. It does not mean that 97.2% of vehicles had a problem, or that purchase risk fell by 2.8%.

How the experimental formula works

First, multiply the component rates by their weights and add them. Then divide that result by the equivalent measure for the 2023 reference and multiply by 100. These weights are editorial choices, not estimates of loss severity or independently validated predictive importance.

Odometer anomalies are excluded because their coverage changed. Exclusion avoids that particular discontinuity, but does not establish that the remaining components have fully consistent coverage or composition.

Historical observations in context

Annual and monthly rows describe different windows and should not be read as a single continuous monthly sequence. An incomplete year is also not directly equivalent to a completed year. No seasonality, vehicle-mix adjustment or uncertainty interval is supplied.

The earlier statement that September was the first reading below 100 since early 2025 was incorrect: August was already 99.8. That statement is removed. The September observation must also remain labelled as partial.

What can change the index without changing an individual car

A different mix of trucks, passenger cars or motorcycles can change the component rates. The same can happen when more customers check newer vehicles, when a vehicle is checked repeatedly, or when a source returns a field differently.

Those possibilities are not quantified in this series. A movement therefore cannot be attributed to weather, lending behaviour, criminal activity or the quality of vehicles on sale. Establishing those relationships would require additional analysis.

Nor does an index below 100 give a buyer permission to skip checks. The reference is simply a past weighted value, not a safety threshold.

Use the component evidence for a transaction

For a shortlisted vehicle, examine identity, current security-interest information, available history, registration and physical condition. If finance is registered, use the settlement guide. For a repair record, use the written-off vehicle guide.

For stock purchasing, retain the certificate and the evidence resolving each exception. An aggregate monthly indicator cannot authorise release of a vehicle with unresolved identity or finance questions.

Quoting or extending the series

Describe this as an experimental historical AUCN check-record index, state the reference and include the cutoff. Do not call the September observation a completed month or a current October reading.

There is no automatic monthly publication commitment. A future extension would need consistent field definitions, complete-period handling, repeat-search treatment and vehicle-mix analysis. The methods page explains the existing limits, and the research hub links to the individual measures and practical guides.