IS A POPULATION CENSUS?
In its most basic form, a population census
is an account of the number of inhabitants in
a country or territory. Census taking has its
beginnings in ancient times and was undertaken
primarily for taxation purposes. From
these early population counts, the modern census
evolved from around the seventeenth century,
with the characteristics of universal coverage,
wide scope of inquiry and provision of information
for statistical and planning purposes.
Today, despite the availability of administrative
records on the population, most countries still
conduct the conventional census through field
work to obtain data on the size of the population,
its characteristics and its distribution across
the various areas within the country.
In addition, most countries combine a population
census with a census on housing to obtain data
on housing conditions.
IMPORTANCE OF CENSUS TAKING
The population census is probably the most
comprehensive source of information on population
and households. It meets a variety of
needs and provides benchmark data for all demographic,
social and labour force statistics. As a result,
the census is usually considered an exercise
of national importance. It requires the participation
and cooperation of every person in the country
and the results of the census are widely disseminated.
TAKING IN SINGAPORE
Singapore's first census was taken in April
1871 as part of the Straits Settlement Census.
Since then, regular censuses were undertaken
at ten-year intervals up to 1931. The Second
World War delayed the next censuses till 1947
and 1957. Singapore's first population census
after independence was conducted in 1970. The
next two censuses were conducted in 1980 and
Census taking in Singapore is in line with
the recommendation of the United Nations (UN)
that a national census be taken at least once
every 10 years. As the value of census data
is increased if it can be compared internationally,
the UN has recommended that countries may wish
to undertake a census in years ending in '0'
or as near to those years as possible.
1970 AND 1980 CENSUSES
In the 1980 Census and earlier, census information
were collected by field work, i.e. home-to-home
visits. In the first stage, houses were numbered
on-site to ensure complete coverage. The second
stage involved a large number of field interviewers
visiting households to collect the information
and to record them on paper forms. The third
stage was conducted on the designated census
reference day to confirm the number of persons
in each house and the validity of entries recorded
earlier in the census forms. The large
volume of information collected was then processed
through a cycle of coding, data entry, verification
and table generation.
In all, 2,015 enumerators were employed in
1970. In 1980, some 2,200 enumerators were mobilized,
including 500 full-time NS men who assisted
in census field work and data processing.
The 1990 Census tapped the potential of using
Unique Identification Numbers (UIN) of every
citizen and permanent resident, and Foreign
Identification Number (FIN) for every foreigner
for record linking with government databases.
Information on level of education attending,
and highest qualification attained was merged
with basic demographic and personal particulars
of each individual to form the pre-census database.
As far as possible, the census forms were pre-printed
with data from the pre-census database for verification
Field interview remained the main method of
data collection. In all, about 3,500 census
workers were involved. As in the 1980 Census,
the data collected were processed through a
cycle of coding, data entry, verification and
FOR CENSUS 2000
After the 1990 Census, the Department of Statistics
reviewed the entire framework in which social
and demographic statistics were collected and
used with a view to improve the methods and
procedures for Census 2000.
Three important exogenous trends have been
identified as having a profound influence on
the collection of social and demographic statistics.
First, the demand for comprehensive data on
the population on a timely basis has been increasing.
Secondly, the advances in Information Technology (IT) including the wide spread use
of Internet, data warehousing software and integrated
call-centre technologies have opened up new
possibilities in data collection and capture.
Thirdly, the stability and reliability of public
databases developed in the 1980s meant that
a large amount of administrative data could
be matched, captured and used for statistical
A REGISTER-BASED CENSUS 2000
With the three major trends in mind, a Household
Registration Database (HRD) was set up in March
1996 to provide up-to-date information between
the censuses. The ultimate aim is to conduct
an administrative register-based census in the
The HRD captures basic personal and demographic
data and updates them by linking with existing
government databases through the UIN. With the
improvement in IT technology and the experience
gained in the 1990 Census, the development of
the HRD proceeded as planned. It is expected
to be fully functional by late 1999.
In many countries, a population census is conducted
together with a housing census to find out the
characteristics of dwelling units. Since
1980, DOS maintains an up-to-date database on
dwellings. In 1996, this database was upgraded
and renamed National Database on Dwellings (NDD).
The NDD and HRD together give a physical location
for every household in Singapore.
The value of Census data lies in its comprehensive
coverage and simultaneous time reference. Since
basic data items (e.g. sex, age, ethnic group,
nationality and type of house) on the entire
population are already available from the HRD
and NDD, it would suffice to conduct a register-based
census. Additional data required for in-depth
studies will be collected from a large sample
of the population with the same reference period.
Experience from the past censuses and sample
surveys indicates that a 20% sample enumeration
of households would provide sufficient details
for in-depth studies and meet the needs of the
majority of users.
Confidentiality of the HRD
In the process of merging some administrative
databases to set up the HRD, the basic personal
and demographic information of individuals and
households are stored in a single repository.
Individual information in this Database is protected
under the provisions of the Statistics Act,
which strictly prohibits the release of any
individual or household information by the Department
of Statistics to any person or agency. Only
aggregate statistics could be released from
the database for statistical and analytical
TRI-MODAL DATA COLLECTION STRATEGY
In the 2000 Census, the basic population characteristics
such as age, sex, ethnic group, nationality
will come from the register. For the 20% sample
enumeration on additional topics, Census 2000
will exploit the possibilities offered by the
IT advances by adopting a tri-modal data collection
strategy. This comprises Internet enumeration,
Computer Assisted Telephone Interviewing (CATI)
and field work (with mail-back option).
Singapore will be the first country in the
world to attempt collecting Census information
from households via the Internet. Several issues
and concerns need to be addressed when making
this bold step. It is recognized that the onus
is on the respondents to self-enumerate via
the Census 2000 Internet website. To achieve
a sizable response, the design of the online
Census form, incentives and publicity would
be critical success factors. Furthermore,
since a sample of the household database will
be open for online public access, security and
confidentiality issues will have to be addressed
in order to prevent unauthorized access, hacking
or denial of service attacks.
It is assessed that the advantages of Internet
Enumeration outweigh the potential risk factors.
Respondents enjoy greater privacy, as their
information will be transmitted directly to
the Department's database. Furthermore, the
form-filling experience over the Internet will
be a positive and interactive one. When the respondent
logs in to the Census website, some basic data
already available in the pre-census database
will be displayed. The respondent could then
proceed to fill up the rest of the census questionnaire
on-line. User-friendly help features and
explanatory notes will be provided instantaneously when
required. The system will also perform simple
on-line checks, and prompt the respondent to
re-enter data that are clearly wrong or inconsistent.
For further convenience, partially completed
questionnaires could be saved and retrieved
at a later time for completion.
From an operational perspective, Internet enumeration
has many advantages. Most of the data
collected from the Internet would already
be electronically coded, thus reducing data
entry and coding at the back end. Furthermore,
there are substantial manpower savings since
interviewers are not required to "canvass" information
from the population.
Computer Assisted Telephone Interviewing (CATI)
operations will commence after a suitable time
lapse following the launch of Internet enumeration.
Unlike Internet, CATI is a tried and tested
data collection strategy, having been deployed
for the mid-decade General Household Survey
in 1995 where some 40,000 households were successfully
enumerated by telephone.
Households selected will be distributed evenly
by postal districts (Pds). For each PD,
households that have not submitted their returns
by Internet will automatically be scheduled
and dialled up for CATI interview.
Records will be scheduled for field work if
the households could not be contacted by CATI
after a number of telephone attempts. These
records will be grouped by PDs and passed to
regional census offices. Field workers
will visit these remaining households to conduct
face-to-face interviews. Should they fail to
contact these households, they will leave blank
census forms with these households who could
fill and mail the forms back to Census Office.
Confidentiality and Security
The tri-modal data collection strategy means
that the collection of personal and household
information for the majority of the population
will no longer be conducted face-to-face. As
such, data confidentiality and security issues
are of paramount importance to the Department
To ensure confidentiality, all selected households
will receive a notification letter with a unique,
randomly generated password. Using the password
and the UIN, respondents who wish to be enumerated
by Internet would be able to log-on to their
household record in the database via the Census
website. The checking of the password shall
be performed in a secure manner with Privylink.
This uses the password as a key to generate
a random sequence at the respondent's computer.
This random sequence is then transmitted over
the Internet. As the respondent's password is
not sent across the Internet, the password cannot
be intercepted and read. At the server end,
the random sequence received is decrypted with
a key server. If the decrypted sequence matches,
the respondent is authenticated and granted
All personal information provided by respondents
would be at least 128-bit encrypted before transmission
over the Internet. This protects the information
from unauthorized interception. To protect the
information from hacking, a DMZ (Demilitarised
Zone) utilising two layers of computer firewalls
would be set up to protect the on-line database
in which the information is stored. These security
measures would be subjected to the most stringent
tests and shall conform to NCB's computer security
For CATI, census interviewers would quote the
respondent's unique password over the telephone
to identify themselves as genuine census officers
before proceeding with the interview. When in doubt over the identity of the CATI
interviewers, the public could also call the
census hotline for verification of their identity.
The register-based approach to Census 2000,
supplemented by a large-scale 20% survey will
mark a watershed in the history of census taking
in Singapore. For the first time since
1871, information will no longer be "canvassed"
from the entire population. This approach is
not entirely new. It has been the practice of
statistically advanced countries which maintain
population registers, such as Denmark, Finland,
Norway, Sweden and the Netherlands.
Outside of Europe, Singapore will be the first
country to embark on the register-based approach.
In deciding to move in this direction, DOS had
studied three key issues. First, the quality
of administrative data in Singapore is sufficiently
high to produce an accurate count of the population
and its basic characteristics. Secondly, the
legal environment and data confidentiality practices
in Singapore permit the sharing of non-sensitive
administrative information. Finally, the
cost savings in adopting this approach are substantial.
It is estimated that the cost of conducting
a register-based census, coupled with a large-scale
survey, is less than one-half of the cost of
a full-scale census.
It is worthwhile to note that of the
163 censuses taken in 1990 round, only 23 countries
used more than one method of data collection,
namely face-to-face interview and delivery-collect.
Of these, only 2 countries adopted a combination
of three data collection methods viz face-to-face
interviews, delivery-collect as well as mail-out
collect. The tri-modal data collection strategy
adopted for the 20% sample enumeration in Singapore's
Census 2000 is a bold experiment in multi-mode
data capture and the application of cutting-edge
information technology. DOS views the integration
of the various modes as a critical success factor
for Census 2000. To ensure smooth workflow
and seamless transfer of data from one mode
to another, a census management system will
be developed to track the progress and ensure
completion of each phase.
Beyond 2000, DOS will look into a system
of continuous measurement of social, economic
and demographic indicators by tapping the records
of the HRD and the NDD. A system of regular
small-scale surveys could be put in place to
collect information not obtainable from administrative
sources and to monitor population and social
trends of current interest.