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Population Pyramid

Dashboard Guide

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Voting Age Population Pyramid

Dashboard Guide

New Voters Calculation Methodology

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What are 'New Voters'?

New voters are people who become eligible to vote for the first time in each election. These are individuals who turn 18 years old between election cycles, representing the fresh cohort entering New Zealand's electorate every three years.

How are they calculated?

Identify the target group: People who will turn 18 between the previous election and the current election
Find the base year: Three years before the current election (when our target group was aged 15-17)
Extract population data: Sum of people aged 15, 16, and 17 in the base year
Apply demographic filters: Filter by selected ethnicity (Total, Māori, Non-Māori) and projection scenario

Example: 2029 Election

Current election: 2029
Previous election: 2026
Base year: 2026 (3 years before 2029)
Target group: People aged 15-17 in 2026
Logic: These individuals will turn 18 between 2027-2029
Result: Sum of 15, 16, and 17-year-olds from 2026 = New voters in 2029

Data Sources

National projections: Stats NZ population projections (2018-2043) with uncertainty ranges (25th, 50th, 75th percentiles)
Regional projections: Stats NZ subnational projections with interpolation for intermediate years
Quality: Official demographic projections based on births, deaths, and migration patterns

Important Considerations

Assumptions:

Elections continue on 3-year cycles
Population projections are accurate
No major changes to voting eligibility
Uniform age distribution within age bands

Limitations:

Not all 18-year-olds may be citizens or eligible to vote
Not all eligible people register to vote
Not all registered voters actually vote
Population projections have inherent uncertainty
Regional estimates use interpolation for some years

How to interpret these numbers:

Conservative estimate: Use 25th percentile for lower-bound projections
Best estimate: Use 50th percentile for most likely scenario
Optimistic estimate: Use 75th percentile for upper-bound projections
Regional variations: Urban areas typically have more new voters than rural areas
Demographic differences: Māori population generally has a younger age structure

Data Interpolation Methodology

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Why is interpolation needed?

The official subnational population projections provided by Stats NZ are typically released for specific years, often at 5-year intervals (e.g., 2023, 2028, 2033, 2038, 2043). However, we need population estimates for years that fall between these official projection points to analyse the potential voting-age population for specific election years (2026, 2029, 2032, 2035, 2041). Interpolation allows us to estimate these intermediate values.

How is linear interpolation performed?

This tool uses linear interpolation to estimate the population for the required election years. Here's how it works:

Grouping: The population data is grouped by unique combinations of Region (Area), Ethnicity, Sex, Age Band, and Projection scenario (Medium projection is used for this analysis).
Finding Bracketing Years: For a target election year (e.g., 2029) that does not have official data, the function identifies the closest available projection years before (e.g., 2028) and after (e.g., 2033) within each specific demographic group.
Estimating Population: It assumes a straight-line (linear) change in population between the known data points (e.g., between 2028 and 2033). The population for the target year (2029) is then calculated based on where it falls proportionally along that straight line.
Applying to All Groups: This process is repeated for every combination of region, ethnicity, sex, and age band to build a complete estimated dataset for the target election years.

Example: Interpolating for 2029

Available data: 2028 and 2033 projection points
Target year: 2029
Position: 2029 is 1 year into a 5-year span (1/5 = 20% of the way)
Calculation: Population₂₀₂₉ = Population₂₀₂₈ + 0.2 × (Population₂₀₃₃ - Population₂₀₂₈)
Result: Estimated population for 2029 based on linear trend

Quality Considerations

Strengths:

Based on official Stats NZ demographic projections
Maintains consistency across demographic groups
Simple, transparent methodology
Preserves demographic trends from official projections

Limitations:

Assumes linear population change between projection points
Cannot account for unexpected demographic events
Less accurate for areas with highly variable population trends
Interpolated values are estimates, not official projections

Purpose and Interpretation:

Purpose: This interpolation provides the best available estimate for the voting-age population structure in specific election years based on the trends shown in the official 5-yearly projections. It allows for meaningful analysis even when official data for the exact year of interest is unavailable.

Interpretation: Use interpolated estimates as indicative values for planning and analysis purposes. For the most precise demographic projections, refer to the official Stats NZ projection years.

More Information

Working Age Population Pyramid

Dashboard Guide

Population Demographics Explorer

Interactive Analysis of New Zealand's Demographic Future

About This Application

This interactive tool visualises New Zealand's projected demographic changes from 2018 through 2043, providing insights into both total population and voting-age population trends across national and regional levels.

Key Features:

Interactive Population Pyramids: Explore age and gender distributions with hover details.
Regional Analysis: Compare demographic trends across New Zealand's regions.
Ethnicity Breakdowns: Analyse Total, Māori, and Non-Māori population projections.
Electoral Insights: Examine voting-age populations and new voter estimates.
Data Export: Download selected data and complete datasets for further analysis.
Multiple Projections: View low, medium, and high projection scenarios.

Data Sources:

Population projection data for Aotearoa New Zealand used in this application has been sourced from Stats NZ's Aotearoa Data Explorer . The national and regional populuation projections were obtained from the 2018(base)-2043 data sets.

About iNZight Analytics

Background & Purpose

We help you use data to tell your story. Decision-makers need to collect, access, and understand data to make informed choices. We design new data-collection and analysis tools, improve access to existing data, and increase data literacy.

We design our data services and research based on your needs, rather than just producing datasets and software. With extensive experience as data users, we create approaches that work for users first — then we handle the technical complexities.

Our Services

Data Collection Design: Efficient, effective research projects tailored to your needs, including Māori research perspectives.
Data Analysis: Specialising in applied social and epidemiological analysis, including Statistics New Zealand Integrated Data Infrastructure.
Training & Education: Making data learning fun, accessible, and relatable through workshops and courses.
Data Sovereignty: Supporting communities in research design that meets their goals and aspirations.
Visualisation & Storytelling: Creating interactive tools that make data accessible whilst keeping it secure.
Consulting: From project management to hourly advisory work.

Data for tāngata, by tāngata, with tāngata. We help communities design research that meets their aspirations, providing guidance on research design, planning, and Māori data sovereignty decision-making.

Application Authors

Eric Marshall and Andrew Sporle
iNZight Analytics

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This application demonstrates iNZight Analytics' commitment to making complex demographic data accessible and actionable for decision-makers across Aotearoa New Zealand.

Population Demographics Explorer

Please select a demographic dataset to explore:

Aotearoa Demographics

Pacific Island Demographics

Select Year:

Select Population:

Select Geography:

Select Region:

Select Projection:

Right Panel Display:

Export Data:

Dashboard Guide

Select Election Year:

Select Population:

Select Geography:

Select Region:

Select Projection:

Display Population:

Right Panel Display:

Export Data:

Dashboard Guide

New Voters Calculation Methodology

What are 'New Voters'?

How are they calculated?

Example: 2029 Election

Data Sources

Important Considerations

Assumptions:

Limitations:

How to interpret these numbers:

Data Interpolation Methodology

Why is interpolation needed?

How is linear interpolation performed?

Example: Interpolating for 2029

Quality Considerations

Strengths:

Limitations:

Purpose and Interpretation:

Select Year:

Working age group:

Select Population:

Select Geography:

Right Panel Display:

Export Data:

Dashboard Guide

Population Demographics Explorer

Interactive Analysis of New Zealand's Demographic Future

About This Application

Key Features:

Data Sources:

About iNZight Analytics

Background & Purpose

Our Services

Application Authors