Applications: Imputation of MĀori Descent for Electoral Calculations in New Zealand

The New Zealand Government Statistician decided that, for electoral purposes, Statistics New Zealand should impute Māori–descent status for individuals not responding Yes or No to theMāori–descent question in the 1996 Census of Population and Dwellings. Imputation provides a sounder basis for calculating electoral populations than the approach used in 1994, when all who had not answered clearly Yes or No in the 1991 Census were effectively allocated to non–Māori descent. For the purposes of imputation, the key variables related to the Māori–descent variable were identified using a statistical technique called CHAID (Chisquared Automatic Interaction Detector). Subgroups were created by cross–classification across five variables—island, iwi, Māori ethnic group, Māori–descent composition of the rest of the household, and age group. Within each subgroup, the proportion who responded Yes or No for Māori descent was used to allocate the remainder to Yes or No. The imputation increased the proportion allocated to Māori descent from 16.0% to 17.4% of the total population. However, the proportion of the population imputed to Māori descent was smaller than the proportion who specified Māori descent originally.