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New Zealand Income Survey: June 2015 quarter
Embargoed until 10:45am  –  02 October 2015
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

Population rebase and introduction of regional benchmarks

The New Zealand Income Survey (NZIS) is a sample survey. We use statistical weights to calculate income estimates for the total New Zealand population. Following each census we revise the weights, to make use of the latest population counts. This process is called a population rebase.

Regional benchmarks enable better estimates of income by region. They work by adjusting the statistical weights, so that the known number of people within each region is maintained.

On 31 August 2015 we implemented the population rebase and regional benchmarks for the NZIS. This resulted in the revision of income estimates from 1997–2014. The revised estimates are available on NZ.Stat.

See New Zealand Income Survey population rebase: June quarters 1997 to 2014 for more information about the revisions.

External data influencers

We collected data in this release in the June 2015 quarter (6 April to 5 July 2015).

Changes in income may be influenced by one-off events. Events that could have influenced the June 2015 quarter data are:

  • the increase in the adult minimum wage from $14.25 to $14.75 (effective from 1 April 2015)
  • increases in government transfer maximum rates of 0.51 percent for main benefits and student allowances (effective from 1 April 2015)
  • increases in New Zealand Superannuation rates of 2.07 percent (effective from 1 April 2015).

Response rates to 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 2015 quarter was 88.3 percent.

We calculate the response rate 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 2015 quarter.

 New Zealand Income Survey response rates, by major sub-populations, June 2015 quarter

Demographic

Response rate (%)
 Sex
 Male      87.3
 Female  89.3
 Ethnicity
 European  88.7
 Māori  86.3
 Pacific peoples  86.7
 Asian  87.0
 MELAA(1)  82.0
 Other ethnicity  91.5
 Labour force status
 Employed 86.3
 Not in labour force 92.0
 Unemployed 93.0
 Full-time employed 86.0
 Part-time employed 87.3
 Overall 88.3
 1.MELAA-Middle Eastern/Latin American/African.
 

Sampling errors

The table below summarises the main sampling errors for the June 2014 and June 2015 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 2014 and June 2015 quarters
 Income source Sampling error (%)
   2014 
 2015 
 Average    
 Wages and salaries  3  2
 Self-employment  13  9
 Government transfers  2  2
 Investments  13  9
 Other transfers(1)  22 22
 All sources collected  2  2
 Median    
 All sources collected  2  2
 1.Other transfers includes private superannuation and annuities.

Contact info@stats.govt.nz for more detailed sampling errors.

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 30,000 individuals. 

We ask all respondents to the HLFS 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. We collect the following items:

  • 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 '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 received from investment
  • total annual gross income received from all income sources (income ranges are the ones used in the 2013 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.

See flowcharts for the NZIS questionnaire. The 2015 flowchart was the same as the 2014 one.

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. We revised the method for calculating sampling errors in 2012.

Contact info@stats.govt.nz for more information about sampling errors.

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

Where possible, the NZIS gets information directly from each household member. However, 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).

The proxy rate for the June 2015 quarter was 20.1 percent. This compares with 20.3 percent in the June 2014 quarter.

Sample design information

Because the NZIS is a supplement to the HLFS, it uses the same sample design. We select the sample 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 surveys can be as high as one half, and some households can be asked the NZIS questionnaire twice. 

Imputation

For records where there is not a valid and usable response, we use a form of imputation known as 'hot-deck imputation'. 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.

We construct imputation pools 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.

We use hot-deck imputation 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.

The imputation rate for the June 2015 quarter was 11.1 percent. There is little change in the income distribution or average income figures in the dataset due to imputation.

Contact info@stats.govt.nz for further information about the imputation method, or the effects of imputation on the final dataset.

Consistency with other periods or datasets

Highest-qualification statistics

In the June 2013 quarter we updated the HLFS qualification response options. The response options now ask respondents to supply the level of the qualification (eg level 4) they obtained, rather than the type of qualification (eg national certificate in business). As a supplement to the HLFS, we changed the NZIS highest-qualification output categories to reflect this.

In previous years, the vocational or trade qualification category captured all levels of certificates and diplomas obtained since leaving school. From the June 2013 quarter, these qualifications are grouped by their level. This means those who obtained their highest post-school qualifications at level 1, 2, or 3 are now included in the NCEA level 1, 2, or 3 or equivalent categories. Also, those who gained certificates or diplomas at level 7 are output to bachelor’s degree / level 7 category.

Adopting the new highest-qualification output categories gives a continuity break in the highest-qualification series as the old output categories are no longer produced. Therefore, the June 2013 data onwards is not directly comparable with previous years.

In the June 2014 quarter, we made some improvements to the highest-qualification output categories to better meet our customer needs. This means that the June 2014 quarter highest-qualification data is not directly comparable with the June 2013 data, or with previous years. 

Self-employment income questionnaire change

In the NZIS, if a self-employed respondent cannot provide their current or previous year’s net profit/loss, we ask them to estimate this amount by indicating whether they receive greater than or less than a series of income values. For example, a respondent may receive a net profit that is greater than $20,000, but less than $25,000.

In the June 2013 quarter, we updated the self-employment income values to reflect changes in the pattern of self-employment income received. Previously, the values started at greater or less than $30,000. However, from the June 2013 quarter onwards, the values begin at $35,000.

See the self-employment flowchart for the June 2013 quarter for more details. The changes are written in red.

In the June 2013 quarter, 17 percent of respondents estimated their self-employment income using these values. The updated values had no major impact on self-employment income and, therefore, the self-employment income data is still comparable with previous years.

Contact info@stats.govt.nz for more information about this change.

Industry statistics

Since the June 2010 quarter, we have based industry statistics 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.

See Industrial classification for more information.

Occupation statistics

Since the June 2010 quarter, we have used the Australian and New Zealand Standard Classification of Occupations (ANZSCO) 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.

See Occupation for more information. 

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, we count people who report more than one ethnic group 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.

We have used the total response method 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. We can only produce the total response ethnicity series for 2008 onwards.

See Statistical Standard for Ethnicity – 2005 for more information about the 2005 New Zealand Ethnicity Standard Classification.

Computer-assisted interviewing

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

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. We interview seven-eighths of the sample by computer-assisted telephone interviewing and one-eighth by computer-assisted personal interviewing.

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 also includes 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 people who are likely to be in the labour force, and couples and single people 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 population's composition 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.

See User guide for wage and income measures for more information on income measures at Statistics NZ.

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 that represent fewer 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. We may remove records 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. We can customise data requests to users' specifications.

Contact info@stats.govt.nz for more information about customised data.

More information

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

See 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 request information from us

Statistics in this release have been produced in accordance with the Official Statistics System principles and protocols for producers of Tier 1 statistics for quality. They conform to the Statistics NZ Methodological Standard for Reporting of Data Quality.

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

Our information releases are delivered electronically by third parties. Delivery may be delayed by circumstances outside our control. Statistics NZ accepts no responsibility for any such delay.

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