Finding the crowding index that works best for New Zealand: Applying different crowding indexes to Census of Population and Dwellings data for 1986–2006 (Stats NZ WP 11-04)

This study aimed to determine which household crowding measure worked best in the New Zealand context.

The issue of crowded households has concerned researchers in New Zealand in recent years, particularly because of the relationship between crowding and ill-health. Research shows that the incidence of close-contact contagious diseases, such as meningitis and bacterial pneumonia, rises sharply in the most-crowded areas.

There is no standard measure of crowding used internationally, but in New Zealand the Canadian National Occupancy Standard (CNOS) is often used as a de-facto standard. However, uncritical use of this standard has generated some controversy. This is particularly in the health sector, largely around the question of the ‘cultural appropriateness’ of this and other crowding measures.

Different quantitative crowding measures were applied to New Zealand census data. Investigations involved assessing data quality, examining a cultural fit with the New Zealand context, and exploring the results of analysis. Crowded populations were compared to see whether characteristics of people and households, or the geographic distribution of crowding, varied by index. This process involved data analysis and also discussion of crowding concepts with agencies that deal with housing issues.

Results indicate that the type of index used substantially affected the number of households and people identified as living in a crowded household. The percentage of crowded households varied from 2.7 percent (American Crowding Index) to 6.9 percent (Equivalised Crowding Index). This variation shows the importance of understanding the impact that different definitions of crowding can have when enumerating the extent of crowding within a population.

The characteristics of crowded households, however, were broadly similar regardless of the index used. The type of index did not really affect the ethnic or geographical distribution of crowding.

Determining which crowding index was most effective largely depended on two aspects: data quality and cultural fit within New Zealand norms. The Canadian National Occupancy Standard appeared the ‘best fit’ within the New Zealand context. However, presenting figures for more than one crowding index enables international comparisons to be made.