Innovations on methods and survey process for the 2011 Italian population census

1. Innovations on methods and survey process for the 2011 Italian population census European Conference on Quality in Official Statistics 8-11 July, 2008 Giancarlo Carbonetti, Marco Fortini, Fabrizio Solari

2. European Conference on Quality in Official Statistics Italian Census and municipal population registers • Italian census can be defined register improved • Conventional methodology • Check against population register, followed by follow up • Population registers enlist people dwelling in Municipalities • Are managed locally • Record vital and internal/external migration events • Are used in updating population between two censuses • New census strategy aims in improving • Integration between census and population registers • Field organization and timeliness

3. European Conference on Quality in Official Statistics Size as the most critical factor for data quality Organizational impact strongly dependent on the size of the municipality  demographic size as one of the most important risk factors in the past census round As a result, it will be considered a modularity for the innovation scheme which depend on the municipalities population size

4. General Scheme for largest municipalities (A and B) European Conference on Quality in Official Statistics Source 1) Municipal Population Register (called LAC) Source 2) Auxiliary Sources Information Lists (called LIFA) Source 3) Addresses Register (called RNC) • Units included in LAC • mail out of partiallyprefilled questionnaires • multi-mode response (mail back, web, Cati) • Enumerators field work: • late respondents collection • check for over-coverage • Units not included in LAC • option 1: complete search of missing units by enumerators on the basis of LIFA and RNC • option 2: survey based on capture recapture and adjustment of census counts

5. European Conference on Quality in Official Statistics Use of samples of households for long form enumeration • Mail out of census forms requires lighter questionnaires so as to • Increase the spontaneous response rate • Reduce as much as possible the response time delay • Less enumerators will be necessary to retrieve information But using only short form would decrease census informative power • Census variables are partitioned into two mutually exclusive subsets • demographic variables, such as gender, date of birth and nationality • socio-economic variables, such as educational level, occupational status and commuting • Random sampling from population registers • Sample of households provided with long forms • Remaining households provided with short forms

6. European Conference on Quality in Official Statistics Sampling design and estimation domains • Domains: national, regional, provincial, municipal and sub-municipal • Sub-municipal areas define a partition of municipal urban territory, each of about 15,000 inhabitants • For 504 Italian municipalities with 20,000 inhabitants or more (or Chief Towns), at least an urban area can be built Sampling from population registers • Municipalities greater than 20,000 inhabitants • urban areas: long forms sent to a sample of households and short forms sent to remaining households • rural areas: long form sent to all the households residents • Municipalities between 5,000 and 19,999 inhabitants • municipal level: long forms sent to a sample of households and short forms sent to remaining households (not yet decided) • In municipalities smaller than 4,999 inhabitants long forms are sent to the whole residents.

7. European Conference on Quality in Official Statistics Experiments • Goal: evaluating the expected efficiency of sampling estimates • Carried out on 2001 census data • 40 municipalities with at least 10,000 inhabitants (15 ≥ 100,000) • Chosen not randomly • across the country • different populations size • 10% of Italian households considered in analyses • Various sampling rates considered (10%, 20%, 33%) • Multivariate tables of short and long form variables together • Calibrated estimates of 90 absolute and relative frequencies • Sub-municipal (among 5,000 and 15,000 people), to regional domains • Montecarlo techniques simulating sampling distribution of estimates • Comparisons carried out by means of Coefficient of Variation (CV)

8. European Conference on Quality in Official Statistics Main results • Coefficient of Variation (average and maximum expected values) for the estimates referred to census sub-municipal areas

9. European Conference on Quality in Official Statistics Other results • CV improvement when increasing sampling rate from 10% • to 20%: (33-38%) • to 33%: (53-58%) • Average CV improvement when size of sub-municipal areas increases from less than 10,000 inhabitants to • 10,000-12,000: (14-20%) • More that 12,000: (22-28%) Percentage distribution of estimated absolute frequencies Areas with at least 12,000 people

10. European Conference on Quality in Official Statistics Tackle with small domains and rare populations • So as increasing estimates efficiency, standard small area estimators considered in the Eurarea Project are being studied • Both unit level and area level model based estimators have been tested • Early results show good performance when estimating relative frequencies up to 1% (among 50 and 150 cases for sub-municipal level, depending on their population size) • Reduction of MSE is in between 40% and 80% with respect to calibrated estimators https://www.statistcs.gov.uk/eurarea

11. European Conference on Quality in Official Statistics Undercounting evaluation and integration of missing units • Population register have to be amendedalso by undercount • e.g. those units actually dwelling on the field that are not enlisted into the correspondent population register • About 235,000 was the number of people enrolled in municipal population registers after enumeration during 2001 census • People already residing elsewhere in Italy • People coming from abroad (foreigners are underestimated) • Two options are being studied so to overcome the registers undercount • Complete search of missing units on the field • labour intensive • Capture recapture model based on a sample survey • depending on various statistical hypotheses

12. European Conference on Quality in Official Statistics Option 1 - Complete search of missing units on the field • Use of alternative lists of names and addresses (LIFA) • List of street numbers (RNC) supplemented with information referred to the related housing units • whole number of dwellings (without housing units reserved for business activities) • number of dwellings used as usual residence by households enlisted into the population register (LAC) • LIFA is used to contact the households directly at their address • RNC is used to search for new households only at street number where (1) – (2) > 0 • RNC not available for municipalities under 20,000 inhabitants • complete search supported by the list of the households which already sent back a short/long form

13. European Conference on Quality in Official Statistics Option 1 - Critical aspects of complete search • It works well only if vacant housing units are few or very clustered • Can be used as a method of optimisation when lack of resources prevent the complete investigation of the field • In this case an estimation procedure has however to be considered • Example: Florence - 2001 Census data; • 72% of buildings are fully occupied by resident households. • 90% of remaining buildings contain only up to 3 vacant housing units • these buildings are made by 8.5 housing units on average, against a general average of 5.6 housing units per building • Higher risk of people and households duplication is expected • Demanding use of record linkage techniques

14. European Conference on Quality in Official Statistics Option 2 - Capture recapture estimation based on sample survey • Estimation through a sample survey of the population living in each municipality being not enlisted into the related population register • Not all the municipalities are included in the sample • Simplified field activities and better control of costs • First capture: population register corrected for over-coverage (A) • Second capture: complete enumeration inside a sample of areas • True population count P in a given area can be estimated by • tover rate of not eligible people enclosed into the register • rate of residents non enlisted into the register among those enumerated during the sample survey

15. European Conference on Quality in Official Statistics Option 2- A simplified scheme of the survey in a municipality Municipality areas Some interesting features • Both the tasks can be carried out at the same time • Operational independence between the two procedures is assured • Differently than in the usual Capture Recapture approach, households are contacted only once Check for over-coverage in LAC Check for under-coveragein LAC

16. European Conference on Quality in Official Statistics Option 2 - Sampling scheme • Quite large sample (300,000 – 1,000,000 people) • Direct dual system estimates until regional level • Model assisted estimation for municipal and sub-municipal estimates

17. European Conference on Quality in Official Statistics Option 2 - Some early results on small area estimation • Evaluated through 2001 census post enumeration survey data • 180,000 people and 70,000 households in 98 Italian municipalities • Unit level small area estimation following Wolter (1986) • pi1+ estimated by means of a logistic model on the PES data • Jacknife estimation of the variance is under study • Next step: using an area level approach • Example: Florence

18. European Conference on Quality in Official Statistics Option 2 - Example: Coverage evaluation for Florence

19. European Conference on Quality in Official Statistics Option 2 - Critical aspects of capture recapture approach • Dependencies on statistical hypothesis • Independence between captures, homogeneity • Influence of record linkage errors activities on • Timeliness • Accuracy • Identification of duplicates • Quality evaluation of estimates carried out by the method • Enumeration of housing units and present population • Municipalities population register will not be directly amended for under-coverage • Over-coverage: complete correction • Under-coverage: estimate number of people to be included

20. European Conference on Quality in Official Statistics Concluding remarks • 2011 Census as a step toward a register supported census • Statistical policy and technical issues • Many different methodological issues related each other • Sampling • Modelling • Imputation • Record linkage • Find the trade off among • Innovations • Results comparability • Stakeholder needs • April 2009 – Pilot survey