Symposium 2001/32

12 July 2001


                                                                                              English only



Symposium on Global Review of 2000 Round of

Population and Housing Censuses: 

Mid-Decade Assessment and Future Prospects

Statistics Division

Department of Economic and Social Affairs

United Nations Secretariat

New York, 7-10 August 2001













Population and housing censuses in Italy *

Aldo Orasi and Angela Ferruzza **




.A. Introduction. 1

B. Census development programme and preparation phase. 1

C. New units of enumeration and new units of analysis. 3

D. Monitoring system for the fieldwork. 4

E. Optical reading for data capturing. 4

F. Data processing and data quality analysis. 5

G. Post-enumeration surveys. 5

H. Other symposium issues. 5

References. 8


A. Introduction

1.                  The census can be more relevant to current needs for monitoring progress towards national goals improving the geographical and territorial matters. In fact, the census is the most important opportunity to collect data in small geographic areas. In Italy there is also the unique opportunity to collect detailed information for educational attainment, status in employment and branch of economic activities.


2.                  The international community plays a very important role in ensuring the continuity and maintaining the quality of censuses. In fact, given the very high level of expenses of census operations, it is important that the international community emphasizes the necessity to do the census to collect this kind of information.


3.                  The Italian experience will be described briefly in this paper. But because the Italian population and housing censuses will be held on 21 October 2001, it is important to say that it is too early for Italy to give an evaluation of the situation. Perhaps in the near future ISTAT will have more information to describe the problems encountered and actions taken by census programmes, to speak about advantages and disadvantages of the newly adopted technologies, to explain what it is possible to learn from the current round of censuses, what are the specific areas that need to be targeted as priorities and so on.


4.                  New units of enumeration and new units of analysis will be used in the next Italian census. The census is based on the traditional method of enumeration, with questionnaires delivered to homes by about 100,000 designated enumerators, relying on the local authorities for the fieldwork. A computerized system is monitoring the fieldwork processes. Optical reading will be used for data capturing and the most innovative equipment for data processing. The Internet will be used to disseminate information during the census operations and to disseminate census results at the end of the operations.


B. Census development programme and preparation phase

5.                  The population general census and the general census of dwellings represent the main enumeration about the state of the population and dwellings. In Italy the census is a complete enumeration, and it is conducted every 10 years. It is a direct enumeration, and it is based on the traditional completion of questionnaires by respondents. Therefore, it is a very expensive and irreproducible enumeration.


6.                  With regard to the organization of the census out of ISTAT, besides the ISTAT regional departments, there are some other institutions that will be actively involved in the census execution. Among these, particularly the municipalities will perform an essential role for the success of the census operation.



7.                  Figure 1 shows the external organization of census operations in Italy. With regard to the legal aspects, the population and housing census is based on a Census Law for financing and on a Census Regulation for all the other technical and organizational aspects. Censuses are based also on articles 56 and 57 of the Italian constitution.


8.                  Traditionally the main aims of the population and dwellings censuses are:

·      To cover the total population on a uniform geographic basis and to enumerate the population’s characteristics;

·      To cover the total housing on a uniform geographic basis and to enumerate the housing’s characteristics;

·      To update and to review the population register using population census data; and

·      To determine the legally resident population.


9.                  Taking into consideration past experiences, it would be useful if the municipalities could make comparisons between the census and the population register directly. It is important that the population register of resident persons represent the most important demographic characteristics. Furthermore, the general trend is that of a transition from a questionnaire-based enumeration to a register-based one through progressive mixed solutions.


10.              To test the innovations and modifications for the collection of data in the 2001 Italian census, the following steps have been carried out:


·      Pre-test (April 1998);

·      First pilot survey (25th October 1998);

·      Second pilot survey (April 2000).


C. New units of enumeration and new units of analysis

11.              An important innovation in the next census will be the introduction of new units of enumeration and analysis: “buildings”, on which a specific census will be carried out and, regarding the population census, the “persons temporarily resident” in a dwelling (but usually resident elsewhere).


12.              The availability of a good informative database is important, especially for local public administrators who need to know about the consistency and characteristics of the Italian stock of buildings, their seismic risks and so on. Past censuses took into account only residential buildings (having at least one dwelling), and data were collected from the households living inside. The collected data on buildings were therefore “dwelling attributes”. They were repeated for each household (dwelling) in the building and they were often incoherent. In short, the data did not allow an unequivocal identification and enumeration of buildings. In order to solve these quality problems and to achieve a better knowledge at this unit of analysis, a specific census on buildings will be carried out, using a single form for each building, to be filled in by the enumerators some days before the population census.


13.              One of the most relevant aims of the population census is the “counting” of usually resident persons, so that public administrative registers of the population (called “Anagrafi”) could be revised and updated for each of the 8,100 Italian municipalities. These registers are sometimes old or incorrect, especially because of delays in enrolling and removing people, and they are biased. These biases are to be corrected according to the law on the basis of census counts, and municipalities will have to officially verify whether the census or the population register is correct.


14.              Even if correctly updated, the public register of a municipality may not exactly measure the true number of people living there. In fact, the living habits of certain groups of people make the traditional definition of “resident” quite unsuitable and improper. People like students or employed persons, who spend part of the year or of the week far from their home (living in another place), or persons who spend a long time at their relatives’ house, cannot identify a single place of usual residence, as theoretically required.


15.              A new unit of analysis, the “person temporarily living in a dwelling”, will be used in the Italian census. This is a person who is registered as a usual resident in a certain municipality, where he will be enumerated as a resident, but who lives, lodges or works in a another municipality, where he will be enumerated as “temporarily resident”.


16.              Taking into consideration this kind of residential pattern should also improve data on housing. In the 1991 census a dwelling was classified as “not occupied” if no resident (from the public register) lived there. This criterion overestimated the number of “not occupied” dwellings, which included those occupied by temporary residents. The new definition will better identify houses that are actually empty.


D. Monitoring system for the fieldwork

17.              The census involves great organizational complexity, since the fieldwork of enumeration is delegated to 8,100 municipalities, which are characterized by different demographic sizes, different efficiency and different levels of automation. ISTAT will be supported by its own regional offices to control the performance of census fieldwork. For monitoring census operations a web application was developed to monitor, in real time, census activities and to quickly take measures against anomalies and delays.


18.              Moreover, an auxiliary model computerized system will help the municipalities to carefully control the number of distributed and gathered questionnaires, to compute daily partial aggregation of enumeration units, to summarize data for each enumeration area and to compute the final aggregation of enumeration units.


E. Optical reading for data capturing

19.              ISTAT is going to adopt optical reading for data capturing of census questionnaires and automatic processing for coding some alphabetic variables. In order to realize this plan, the three main stages are entrusted to one single “provider of service”, which will undertake the graphic design of the questionnaires, their printing, transportation (to and from the municipalities) and their scanning.


20.              ISTAT determined that the use of a single provider would avoid the possibility that one supplier could shift responsibilities onto another, in case that the required standards, for any of the different activities (printing, transportation of questionnaires and, mostly, optical reading of the forms) would not be achieved.


21.              Immediately after the scanning process, the main alphabetical variables (name of the municipalities, citizenship, level of education) will be automatically coded, relieving the municipal offices of the burden of a lengthy and difficult clerical coding task.


22.              To assure the best quality of this expensive and important phase, a certified and reliable company will be delegated to perform both the monitoring of the optical reading process and the controls on the quality of acquired data and images.


F. Data processing and data quality analysis

23.              In the census, there are three main stages that modify the data:

·        Identifying the statistical units;

·        Quantitative adjustment; and

·        Editing and imputation operation on the value.


24.              In the first stage we have to transform some sequences of characters that are recorded (we can call it “ physical raw data”) into objects that have some meaning in our context ("logical raw data”).


25.              For the second stage, we need a method to reconstruct total missing values and to identify duplication. Furthermore, we need controls of the territory codes. Also, we aim to have a method to do this automatically as much as possible.


26.              For the third stage, we have to develop methods to correct systematic errors and stochastic errors. In order to do this, we shall use “rules“ to identify and analyse the erroneous data. In imputing the values, we will utilize mainly the probabilistic approach whenever we cannot identify the right value in a deterministic way with a very high degree of confidence. In doing this, we intend to use all the information to determine the right values.


G. Post-enumeration surveys

27.              In order to evaluate census data quality, a survey has been planned to evaluate coverage errors affecting the census enumeration. In particular, both undercoverage and overcoverage errors will be estimated by means of a post-enumeration survey (PES) carried out on a sample of census enumeration areas (CEAs).


28.              This survey is intended to be an external source for controlling the quality of the population census. The results of the control surveys will not be used to correct census data, but simply to provide estimates of the accuracy of the census data. Instead census results will be checked with administrative records from the population register.


H. Other symposium issues

1. Issue 1: Strategies for involving stakeholders in census activities


29.              Who are the stakeholders in Italy? The municipalities will perform an essential role for the success of the census operation. The municipalities are the stakeholders in the collection, dissemination, planning and use of population data. Municipalities have the most important role in the collection of data. But they are also the most important users of data. This is a unique opportunity to collect some of the information about the population and housing for each municipality and for the municipalities divided in enumeration areas. For example, in addition to the number of people, the census makes it possible to know the relationship of persons, educational attainment, current activities status, status in employment, branch of economic activities, information related to journey to place of work or place of study, the number of buildings, the number of dwellings, people living in institutional households and so forth. So municipalities have the unique opportunity to collect and then to use these data. They know this, but ISTAT is trying to involve them in using statistics through national reports, the Internet, and appropriate training classes.


30.              Moreover, Italy has a special commission for the 12 biggest municipalities. In this commission census projects and problems have been introduced and argued about. This commission is continuing its job now and will help during the census operations.


31.              A special census commission comprising many professors and official delegates from institutions collaborated with the census department to project the enumeration structures and contents, to define the dissemination plan and to discuss some methodological aspects. In this commission official delegates of some institutions and of some municipalities have been involved in the selection and development of topics included in the census questionnaire. Data about the 1991 census dissemination were also used in the selection of topics.


32.              In addition, in 1999 a national meeting of the Italian Statistical Society (SIS) was organized on the topic of censuses to suggest and discuss ideas and hypotheses.


2. Issue 2: Strategies for choosing among data-collection methods as sources of demographic and social statistics: censuses, sample surveys and administrative records


33.              Taking into account costs, periodicity, geographic coverage, respondent burden, timeliness, content and statutory considerations, Italy has used traditional census data collection. Sample surveys can give some information but not at the geographic level of enumeration areas. Administrative records have only some of the collected information and at the moment their quality is heterogeneous. Moreover, not all of them are computerized. Perhaps the next census will be the one in which Italy will use a mixed system of traditional methods plus administrative records.


3. Issue 5: Identifying and resolving problems of census mapping


34.              In Italy, as in other countries, the census data-collection process provides a unique opportunity to build complete small-area mapping. Census enumeration areas are called “Sezioni di censimento” (SDC) and SDC features are defined to allow enumerators to easily identify borders of their assigned region, to correctely count statistical units and to avoid any possible double counting. Natural boundaries for SDCs are streets, railway lines and hydrological features such as rivers and lakes.


35.              In 1991 for the first time, an advanced methodology of census mapping was used. “CENSUS”, a complete digital database in ArcInfo format and at a scale of 1:25,000, was developed. It integrated remote sensing images, IGMI maps (Italian National Mapping Agency), technical maps at the regional level and municipality information. “CENSUS” contains administrative boundaries (20 Regions, 95 Provinces and 8,100 communes, corresponding respectively to level NUTS2, NUTS3 and NUTS5 of the European nomenclature); populated localities boundaries (“centri abitati” and “nuclei abitati”) and SDCs (about 330,000) boundaries and coordinates of SDC centroids. Out of 330,000 SDCs in the 1991 census, about 70 per cent were in “centri abitati”, about 10 per cent in “nuclei abitati” and the remaining 20 per cent in “case sparse”. “Centri abitati” and “nuclei abitati” constitute about 10 per cent of the Italian area, and “case sparse” constitute about 90 per cent of the Italian area. With regard to population, 91 per cent is in  “centri abitati”, 3 per cent in “nuclei abitati”and 6 per cent in “case sparse”.


36.              CENSUS 2000 is the mapping project for the 2000-2001 round of censuses. It starts with maps from the 1991 census and combines them with available cartographic data such as digital orthophotomaps, technical maps and vector data from other government agencies, local authorities or private companies. These sources contain a large amount of information on populated areas and such features as streets, rivers and railways. The main objectives of CENSUS 2000 are: i) to redesign and reduce in size census sections in extra-urban areas to get the integration of all census mapping, including for the first time data from the agriculture census. “Case sparse” in 1991 were too big to be used in agriculture and environmental analysis; ii) for the first time, to design economic areas; iii) to improve integration with other territorial databases of public interest; and iv) to use data extraction from digital maps of private companies and local authorities. Four types of populated localites are mapped in the first stage: 1) centri abitati (populated areas), 2) nuclei abitati (small populated areas), 3) località produttive (economic areas) and 4) case sparse (remaining areas). In the second stage, using techniques differentiated for each type of locality, SDCs are mapped.


37.              To fully understand the potential benefit of the census collection process it should be considered not only the output of census data but also all products of the considerable fieldwork, like collection of data on streets, address numbers, and other attributes that can be used in address matching and in geocoding of administrative records. All census outputs can be used in developing strategies of small-area data dissemination. The digital census mapping database can be used for area mapping, and data access via the intranet or the Internet and travel-to-work flow data can be used in functional zones mapping.


38.              Most of the administrative databases contain addresses which allow, when coordinates of address numbers are known, a complete matching of data to points on a digital map. In any case, an address is a respondent identifier and due to confidentiality restrictions, statistical data have to be geographically aggregated.


39.              ISTAT uses a procedure of address matching to link addresses to SDC codes, so that data of each SDC can be aggregated. For each SDC, as an attribute of the SDC polygon, the list of streets is available, and for each street the ranges of address numbers in the SDC, called “Itinerario di sezione” (SDC path). After orthographic correction and normalization of the addresses, the procedure links the SDC code to each address. An important application is the geocoding of the ASIA register (the Italian businesses register). Applications will be extended in the next few years also to geocoding of records from population and social registers, including school and hospital registers.


Chieppa, A., and G. Massimini (1999). Edit and imputation: issues involved in building a system. Proceedings of European Workshop on the Preparation of the Census Fieldwork. Joint ISTAT-ECE-Eurostat Meeting, Rome, 12-14 April.


Chieppa, A., and F. Panizon  (2001). Data quality control system for the 2001 Italian population census. Paper presented at International Conference on Quality in Official Statistics, organized by Statistics Sweden and Eurostat, Stockholm, 14-15 May.


Balestrino, R., F. Baiocchi and A. Reale (1999). Census forms optical reading: taking the opportunity. Proceedings of European Workshop on the Preparation of the Census Fieldwork, Joint Istat-ECE-Eurostat Meeting, Rome, 12-14 April.


Corrado H.C., and D. Zindato (1999): Enumeration structure units of analysis and contents of Italian 2001 Population Census. Proceedings of European Workshop on the Preparation of the Census Fieldwork, Joint Istat-ECE-Eurostat Meeting, Rome, 12-14 April.


Crescenzi, F. (1999): New challenges and opportunities in redesign and updating territorial database. Proceedings of European Workshop on the Preparation of the Census Fieldwork, Joint Istat-ECE-Eurostat Meeting, Rome, 12-14 April.


Egidi, V. (1999). “Le strategie dell’ Istat per i Censimenti del 2000 (Istat strategies for 2000 Censuses). Paper presented at the Conference: Verso i Censimenti del 2000, Udine, 7-9 June.


Ferruzza, A., and S. Mastroluca (1999). Italy 2001 Census development program and the first pilot surveys, Proceedings of European Workshop on the Preparation of the Census Fieldwork, Joint Istat-ECE-Eurostat Meeting, Rome, 12-14 April.


Massimini, G., and P. Valente (1998). Processing the Italian Population and Housing Census data. Paper presented at International Seminar on Census Methodology, Portsmouth (UK), 29 April–1 May.


Vivio, R., (1999). Towards 2001 Italian Housing Census: enumeration structure, contents and proceedings. Proceedings of European Workshop on the Preparation of the Census Fieldwork, Joint Istat-ECE-Eurostat Meeting, Rome, 12-14 April.


*       This document was reproduced without formal editing

**     ISTAT, Italy. The views expressed in the paper are those of the authors and do not imply the expression of any opinion on the part of the United Nations Secretariat