Personal income distribution of 30–34 year-olds in New Zealand

Income is before tax, from regular and recurring sources only. Income figures are collected for those aged 15 years or over. Income groups are deciles (to the nearest hundred dollars) of personal income.
Deciles are formed by dividing the population into 10 groups – ranking individuals by the amount of income they receive. The bottom decile is the lowest 10 percent of the population in terms of income, while the top decile is the highest 10 percent.
People counts are rounded to the nearest hundred. Figures may not sum to stated totals, due to rounding.

Household: is either one person who usually resides alone, or two or more people who usually reside together and share facilities (such as for eating or cooking) in a private dwelling. A household may contain one or more families, other people in addition to a family, or no families at all, such as unrelated people living together.
Housing-costs-to-household-income ratio: is the aggregate housing costs for all households as a proportion of the aggregate household income for all households. This measure is often used as an indicator of housing affordability. However, it is typically calculated by using disposable household income (gross income minus income tax) instead of before-tax (gross) income. Only gross income is reported in this release. This means that the housing costs to (gross) household income ratios may be slightly lower than ratios reported from other data sources. This measure includes households that do not make mortgage or rent payments.
Total housing costs: consists of expenditure from the following sources: mortgage principal repayments, mortgage interest payments, mortgage application fees, rent payments, other payments associated with renting (for example bonds paid in the last 12 months), property rates payments (both regional and local government), and payments associated with building related insurance.

http://datainfoplus.stats.govt.nz/Item/nz.govt.stats/27d850c1-939c-4e93-b61c-a1b5196b7f27

Two types of error are possible in estimates based on a sample survey: sampling error and non-sampling error. The sample size for this survey is approximately 5,500 households, therefore the error for subnational estimates may be significant.

The target population for HES (Income) is the usually resident population of New Zealand living in private dwellings, aged 15 years and over. This population does not include:
- overseas visitors who are in New Zealand for less than 12 months
- people living in non-private dwellings such as hotels, motels, boarding houses, hostels, and homes for the elderly
- patients in hospitals, or residents of psychiatric or penal institutions
- members of the permanent armed forces in group living facilities; for example, barracks
- people living on offshore islands (excluding Waiheke Island)
- members of the non-New Zealand armed forces
- non-New Zealand diplomats and their families.

At URL provided, select "Household Economic Survey (Income): Household income and housing-cost statistics: Year ended June 2018' from under the 'Download Data' heading.

The three main objectives of HES (Income) are to measure patterns of inequality in household income (used for policy-making decisions); measure people’s life satisfaction, housing conditions, and financial stress; provide an indication of the overall living standards of New Zealanders.

HES 2017/18 is the last survey before Stats NZ will increase the sample size to 20,000 respondents. Because 2017/18 is a year in which net worth is also being estimated, it is based on a sample of 5,500 respondents. In years that Stats NZ do not include net worth questions, the sample size is around 3,500 respondents.