A post-enumeration survey (PES) was conducted in New Zealand, following the 2001 Census of Population and Dwellings, to gauge the completeness of census coverage. The main findings of the 2001 PES were:
- About 97.8 percent of New Zealand residents in the country on census night were enumerated in the 2001 Census. This represents a net undercount of 2.2 percent or 85,000 people.
- The net undercount resulted from an estimated undercount of 107,000 people, offset by 22,000 people being counted more than once.
- While the 2001 Census enumerated 3.74 million residents in New Zealand, the PES results suggest that the number of New Zealand residents in New Zealand on census night was closer to 3.82 million.
- The 2001 Census missed more men than women. The undercount rate was estimated at 2.6 percent for males and 1.9 percent for females.
- People aged 15–29 years – the most mobile segment of the population – had the highest undercount (3.1 percent), while those aged 45 years and over had the lowest (1.4 percent).
- Ethnic differentials were marked. Net undercount was significantly higher for Pacific peoples (5.2 percent) and the Mäori population (4.4 percent) than for the Asian (2.4 percent) and European (1.7 percent) populations.
- About 2,400 or 0.2 percent of permanent private dwellings were missed by the 2001 Census.