New Zealand Income Survey: June 2012 quarter

Data quality

Period specific information
Information about data that has changed since the last information release

General information
Information that does not generally change between releases

Period specific information

External data influencers

Data in this release was collected in the June 2012 quarter (8 April to 8 July 2012).

Changes in income may be influenced by one-off events. Events that could have influenced the NZIS June 2012 quarter data are:

  • the increase in the adult minimum wage from $13.00 to $13.50 (effective from 1 April 2012)
  • increases in government transfer maximum rates of 1.77 percent for main benefits and student allowances (effective from 1 April 2012)
  • increases in New Zealand Superannuation rates of 2.65 percent (effective from 1 April 2012).

Response rates to the New Zealand Income Survey

The target response rate for NZIS is 80.0 percent of eligible Household Labour Force Survey (HLFS) respondents. The achieved response rate for the June 2012 quarter was 82.0 percent, or 23,900 of those individuals who were in households that responded to the HLFS.

The response rate is calculated by determining the number of eligible individuals who responded to the survey, as a proportion of the estimated number of total eligible individuals in the sample. The following table shows the NZIS response rates for the June 2012 quarter.

 New Zealand Income Survey response rates, by major sub-populations

Demographic

Response rate (%)
 Sex
 Male       80.6 
 Female  83.2
 Ethnicity
 European  82.5
 Māori  80.3
 Pacific peoples  80.2
 Asian  79.5
 MELAA(1)  83.1
 Other ethnicity  85.5
 Labour force status
 Employed 78.7
 Not in labour force  88.0
 Unemployed  86.1
 Full-time employed  77.8
 Part-time employed  81.4
 Overall  82.0
 1.MELAA-Middle Eastern/Latin American/African.
 

Sampling errors

The table below summarises the main sampling errors for the June 2011 and June 2012 quarters, by income source. See Reliability of survey estimates for more information.

Relative sampling errors for average and median weekly income for all people aged 15 years and over, June 2011 and June 2012 quarters
 Income source Sampling error
   2011
(%)
 2012
(%)
 Average    
 Wages and salaries  3  3
 Self-employment  12  10
 Government transfers  3  2
 Investments  12  15
 Other transfers(1)  26 18
 All sources collected  2  2
 Median    
 All sources collected  3  2
 1.Other transfers includes private superannuation and annuities.

More detailed sampling errors are available by contacting info@stats.govt.nz.

General information

Scope of the survey

NZIS is a supplement to the HLFS and as such uses the same sample population. The HLFS sample has approximately 15,000 private households, sampled randomly from rural and urban areas throughout New Zealand. We gather information for each household member who falls within the scope of the survey and meets the survey coverage rules. The final NZIS dataset has approximately 29,000 individuals. 

All respondents to the HLFS are asked to participate in the NZIS. The target population of the NZIS is the usually-resident, non-institutionalised civilian population of New Zealand aged 15 and over. This population does not include:

  • long-term residents of homes for older people, hospitals, and psychiatric institutions
  • inmates of penal institutions
  • members of the permanent armed forces
  • members of the non-New Zealand armed forces
  • overseas diplomats
  • overseas visitors who expect to live in New Zealand for less than 12 months
  • those aged under 15 years.

New Zealand residents living on offshore islands (except for Waiheke Island), and those temporarily overseas are not surveyed. The survey population is therefore marginally different from the target population.

Survey questionnaire

Questions relate to the respondent's most recent pay period, except for questions on annual income, self-employment income, and investment income, which cover the 12 months before the interview. The following items are collected:  

  • actual and usual gross wages and salaries, for main job and up to two other jobs, by ordinary time, overtime, other income
  • weeks and hours worked, matching the wage and salary components as above
  • sources of latest actual gross government transfers received
  • latest actual gross government transfers received in total and from each agency (Ministry of Social Development, Inland Revenue, and Accident Compensation Corporation)
  • total latest actual gross private superannuation payment(s) received
  • total latest actual gross 'all other private transfers including pensions, and annuities' received
  • weeks covered for the transfer payments defined above
  • total annual gross income received from self-employment
  • total annual gross income from investment
  • total annual gross income from all income sources (income ranges are the ones used in the 2006 Census).

The collected data relates to cash only, pre-tax (gross) income wherever possible and does not include any non-cash fringe benefits.

Questions about some forms of income are not included in the NZIS, for instance income from hobbies, casual jobs, and other sources. Therefore total income estimates from the survey may underestimate actual total income.

In 2005 the NZIS introduced computer assisted interviewing (CAI). Implementation was complete in 2007. During the transition to CAI, estimates for the CAI part of the sample were compared with estimates from the remainder of the sample, and no statistically significant differences were detected.

See here for a copy of the questionnaire flowcharts

Accuracy of the data

Reliability of survey estimates

Two types of error are possible in estimates based on a sample survey: sampling error and non-sampling error. Sampling error is a measure of the variability that occurs by chance because a sample rather than an entire population is surveyed.

Non-sampling errors include errors arising from biases in the patterns of response and non-response, inaccuracies in reporting by respondents (including inaccuracies as a result of proxy interviewing), and errors in recording and coding data. Non-sampling errors are not quantified. We endeavour to minimise the impact of these errors by applying best survey practices and monitoring known indicators (eg non-response).

Proxy

A proxy can provide information under the following circumstances:

  • for a person unable to answer on health or language grounds
  • for a 15- or 16-year-old with an after-school job (parent can respond)
  • for a retired couple whose only source of income is New Zealand Superannuation (one of the couple can respond)
  • for a self-employed couple, or farmer, where one of the couple does the accounts for both (one of the couple can respond)
  • when one person in a couple controls the finances for both (one of the couple can respond).

Sample design information

Sample design

Because the NZIS is a supplement to the HLFS, it uses the same sample design. The sample is selected using a two-stage stratified cluster design. Households are sampled on a statistically representative random basis from rural and urban areas throughout the North and South Islands.

Each quarter, one-eighth of the households in the sample are rotated out and replaced by a new set of households. The overlap between two NZISs can be as high as one half, and some households can be asked the NZIS questionnaire twice. 

Imputation
For those records where there was not a valid and usable response, a form of imputation known as 'hot-deck imputation' is used. In this imputation method, a 'donor record' replaces the non-usable record in the dataset. The donor record is chosen randomly from an imputation pool of records that have similar characteristics to that of the record to be imputed.

The imputation pools are constructed on the basis of the following HLFS variables: age group, sex, ethnicity, highest qualification, labour force status (modified), full-time/part-time work status, and region. Imputation classes are combined in a priority order where there are fewer than 10 donor records in any particular class.

Hot-deck imputation is used for three reasons:

  • to maintain an accurate income distribution of the New Zealand population
  • to allow the calculation and analysis of household income for a larger number of households
  • to account for likely biases due to non-response.

There is little change in the income distribution or average income figures in the dataset due to imputation. For further information about the imputation method, or the effects of imputation on the final dataset, please contact info@stats.govt.nz

Consistency with other periods or datasets

Industry statistics

Since the June 2010 quarter, industry statistics have been based on the Australian and New Zealand Standard Industrial Classification 2006 (ANZSIC06). This aligns with the HLFS. Earlier NZIS releases used ANZSIC96, and are not comparable with those based on ANZSIC06.

For more information please see Industrial classification.

Occupation statistics

Since the June 2010 quarter, the Australian and New Zealand Standard Classification of Occupations (ANZSCO) has been used to classify occupation data. ANZSCO is a harmonised classification for use in both countries. Occupation outputs defined using ANZSCO are not comparable with those in earlier NZIS releases, which were based on the New Zealand Standard Classification of Occupations 1999.

For more information please see Occupation.

Ethnic statistics

Since the December 2007 quarter, the HLFS has collected ethnicity data using the 2005 New Zealand Statistical Standard for Ethnicity, with up to 14 responses captured for the ethnicity question. Under the total response method, people who report more than one ethnic group are counted once in each group reported. This means the total number of responses for all ethnic groups can be greater than the total number of people who stated their ethnicities.

The total response method has been used to publish ethnicity statistics in the NZIS since the June 2009 quarter. Before then, the NZIS used the prioritisation method, where a single ethnic group was assigned to individuals who answered with more than one ethnicity.

Adopting the total response method gives a continuity break in the ethnicity series, as the prioritisation of ethnic groups is no longer produced. The total response ethnicity series can only be produced for 2008 onwards. For more information about the 2005 New Zealand Ethnicity Standard Classification please see Statistical Standard for Ethnicity – 2005.

Computer-assisted interviewing

Since 2007 the NZIS has used computer-assisted interviewing (CAI). The main benefits of CAI are improved data quality through better-controlled interviews, and modest resource savings through eliminating some processing steps and centralising others. Seven-eighths of the sample are interviewed by computer-assisted telephone interviewing (CATI) and one-eighth by computer-assisted personal interviewing (CAPI).

All sources income

The introduction of income from investment in 2002 caused a discontinuity in time series for the 'all sources' category. Before 2002, this category included wages and salaries, self-employment, government transfers, and other transfers. Since 2002, it has also included income from investment and so the category is not comparable with previous years.

Household statistics

The household categories incorporate the concept of dependent children rather than just children. A child is a person of any age who usually resides with at least one parent (natural, step, adopted, or foster), and who does not usually reside with a partner or child(ren) of his or her own. Statistics NZ defines a 'dependent child' as a child aged under 18 years and not in full-time employment.

The household income statistics table in this release excludes households where all members are outside the ages of 18 to 64 years. This exclusion primarily affects 'couple only' and 'one person' households. These households typically contain two distinct groups of the population: couples and single persons who are likely to be in the labour force, and couples and single persons who are primarily retired. Because these groups can have very different income characteristics, the household income table excludes older households where all members are aged 65 years and over (65+). The income figures for 'couple only' and 'one person' households for those aged 65+ are available from Statistics NZ on request.  

Interpreting the data

Compositional effects

Movements in average and median income statistics are influenced by many factors. As well as changes in levels of income, movements are also influenced by the composition of the population from survey to survey. These changes occur between males and females, different ethnic groups, different labour force statuses, numbers of full-time and part-time workers, between or within industries, and between or within occupations.

Income averaged across all people from all sources includes those who have zero income for some income sources. Income averaged across those receiving income from a particular source only includes those who received income from that source.

For more information on income measures at Statistics NZ, please see the User guide for wage and income measures.

Period effects

The NZIS reports on 'weekly income' that relates to a week during the June quarter – it is a snapshot in time. Conversion of this weekly income into an annual equivalent is not recommended as an individual's circumstances can change significantly during a year (eg change of job or a period out of work).

Tables

In this information release, all tables showing wages and salaries include usual income figures rather than actual income figures

Confidentiality and access to the data

Suppressed estimates

Cells which represent less than 1,000 people are suppressed and appear with the symbol 'S' in the tables. These estimates are subject to sampling errors that are too great for most practical purposes. Records may be removed for quality and confidentially purposes in some publications.

Customised data

The tables in this information release are not a full set of the possible analyses that could be carried out from the NZIS data. Data requests can be customised to users' specifications. Please contact info@stats.govt.nz for more information. 

More information

See the New Zealand Income Survey resource page for more information about the NZIS.

See the User guide for wage and income measures for more information about using wage and income measures.

See Information about the New Zealand Income Survey for more technical information.

Confidentialised unit record files (CURFs) for un-rebased 2002–07 NZIS data are available on application. See User guides for Confidentialised Unit Record Files for more information, or use the information request form.

Liability

While all care and diligence has been used in processing, analysing, and extracting data and information in this publication, Statistics NZ gives no warranty it is error-free and will not be liable for any loss or damage suffered by the use directly, or indirectly, of the information in this publication.

Timing

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