Lags in New Zealand's official economic data are creating a fog for policymakers that recently forced them to veer off course and cut interest rates a whole year earlier than projected, badly wrong footing financial markets.

Years of tight funding by successive governments have left statisticians struggling to keep up with a rapidly changing economy, and nowhere more so than with inflation.

The more than two-decade-old system they use is not able to calculate monthly data, making the country rare among developed nations in reporting consumer price indexes (CPI) quarterly, rather than monthly. This makes it harder for the Reserve Bank of New Zealand (RBNZ) to spot turning points in a timely manner.