1. Evaluating imputation of sex and age for substitutes in substitute households Michael Ryan 2008 UNECE Work Session on Statistical Data Editing

2. Overview The New Zealand Census of Population and Dwellings –Background –Dealing with non-response Imputation procedures Estimation of census coverage –Post-enumeration Survey (PES)

3. The New Zealand Census Background –Population size: 4.2 million –Number of households: 1.5 million (in private dwellings) –Census Frequency: every 5 years Organisation –Types of forms –Data collection process

4. The New Zealand Census Dealing with non-response –Within census processes – unit imputation creation of substitute dwelling forms creation of substitute individual forms imputation of sex and age –Outside of census – census coverage survey (Post-enumeration Survey – PES) sample survey to estimate census undercount and overcount

5. Census imputation Creation of substitute households –Characterisation of a missing dwelling Listed in the dwelling frame Classed as a private dwelling Classed as occupied on census night Have no forms received for it –Errors caused by Collectors Processing

6. Census imputation Creation of substitute individuals within substitute households –Donor imputation Random selection From within the immediate physical neighbourhood

7. Census imputation Imputation of sex and age for substitute individuals in substitute households –2001 Census Stochastic imputation from the estimated resident population Sex imputed first (at 51% female to 49% male) Age imputed, conditional on imputed sex

8. Census imputation Imputation of sex and age for substitute individuals in substitute households (cont.) –2006 Census Imputation using the dwelling form

9. Census imputation Imputation of sex and age for substitute individuals in substitute households (cont.) –2006 Census (cont.) Donor imputation for age (from donor household) Stochastic imputation for sex, independently of age

10. Post-enumeration Survey (PES) Objective –Measurement of overcount and undercount in census Additional benefit –Evaluation of imputation in census

11. Post-enumeration Survey (PES) Characteristics –Carried out as independently as possible from the census –Starts 2 weeks after the census –Runs for 2 weeks –Sample size – 11,000 households –Asks for addresses where people were on census night

12. Post-enumeration Survey (PES) What it can do –can identify people for whom substitute forms were created –can estimate number of substitute households that should have been created number of substitute individuals that should have been created, and their distribution by sex and age

13. Comparison of the number of substitutes Comparison between the number of substitutes in Census and PES –Test statistics used (C – P) / SE where C = Census count P = Post-enumeration Survey estimate SE = Sample errors (correspond to 95% intervals) –SE estimation Jacknife methodology using GREG estimates or Based on calculated design effect

14. Comparison of the number of substitutes Number of substitute households and substitute individuals

15. Comparison of the number of substitutes Age and sex of substitute individuals in substitute households

16. Recommendations for 2011 Census That the rigorous checking of the Dwelling Frame against the collectors’ fieldbook that was used in 2006 be continued That further work be done to improve the classification of dwellings as occupied / unoccupied That the current donor household methodology continue to be used to impute the number of census night occupants

17. Recommendations for 2011 Census That sex for full-substitutes be imputed jointly with age That the possible use of PES 2011 estimates of full-substitutes to calibrate substitutes in substitute households be investigated in 2011 Census That the current donor household methodology continues to be used to impute age for substitutes in substitute households

18. Contact Michael Ryan –Michael.Ryan@stats.govt.nzMichael.Ryan@stats.govt.nz