A "misery index" is based on the sum of the inflation rate (CPI) and the unemployment rate. It is a measure than has been around for decades, originally made popular by US President Jimmy Carter.

From a New Zealand perspective, the key value is in the comparative with Australia - unless New Zealand has a lower Misery Index than Australia, and by a significant margin, workers will increasingly relocate from here to Australia.

The income differential may be one important component driving trans-Tasman migration, but the Misery Index will be another.