Transcript Title of Presentation

The new HBS
Chisinau, 26 October 2007
Outline
1.
2.
3.
4.
How the HBS changed
Assessment of data quality
Data comparability
Conclusions
1
Key improvements in the HBS
•
In 2006 the HBS was changed with respect to
two major areas characterising a survey:
1) Sampling: the way in which the sample is selected
was changed in the following aspects:
•
•
•
Sampling frame
Sampling design
Practice of substitution
2) Questionnaires: these were changed to better
monitor poverty and living standards
•
We first look in detail at changes in sampling
and then we explain those related to the
questionnaire
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An old sampling frame
• A sampling frame is the basic structure of information that is used to
draw a sample: population of different villages, cities and lists of
households
• The HBS has been conducted from 1997 to 2005 in the same
enumeration areas (villages and city districts)
• Such enumeration areas were considered to be representative and
were selected based on population information gathered through the
1996 electoral lists (the sampling frame)
• At that time the electoral lists were the best information available,
better than the 1989 Census
• Because of population changes and migration, information in the
electoral lists was becoming increasingly biased, in some villages
the list of households was exhausted
• In 2005 the NBS obtained updated and more comprehensive
information through the 2004 Census as well as a database of
electricity consumers
• Therefore, from 2006 both Census and the electricity database has
been used to select the HBS sample
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Sampling design
• The sampling design defines the main characteristics of the
sample: number of enumeration areas, total number of
households, country regions for which estimates are reliable
• Although the sample size in 2006 is the same as in 2005,
the number of enumeration areas increased from 45 to 120,
thus ensuring a better coverage of the country
• Until 2005 the sample was designed to be representative
for three different regions: cities, towns and rural areas
• Now the sample is representative not only of these three
regions, but also of four economic zones (North , Centre,
Chisinau and South)
• Chisinau and Balti are now better covered and stratified for
low and high income areas
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HBS coverage of Moldova
2005
2006
5
The practice of substitution
• Until 2005 if a household did not want to be interviewed it
was substituted with another household
• This created a selection problem: households with children
tend to refuse interviews more than old people
• From the enumerator perspective some households are
easier to interview and the practice of substitution can
create some distortions, the enumerator may not put all the
efforts in trying to interview the originally selected
households
• The consequence is that the sample becomes less
representative: proportionally more elderly people than in
the actual population are interviewed and this in turn affects
some of the key estimates (consumption, income, etc.)
• From 2006 substitution is no longer allowed and
enumerators are encouraged to interview only the initially
selected households
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Questionnaire improvements
• In 2004 and 2005 the NBS conducted various
experiments in order to improve the questionnaire
design, such experiments guided the changes
implemented in 2006
• Questionnaire changes affected the following areas:
– Changes in the reference period of some income sources and
expenditure items
– Improved layout of the diary (the questionnaire booklet that helps
the household to record income and expenditure transactions)
– Food expenditure recorded only for half a month not the full
month
– Changes in the definitions of employment indicators
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Effects of questionnaire changes
• Collected information can now be used to produce both
accurate averages for the National Accounts, weights for
the consumer price index, and distributional data for
poverty analysis. In particular poverty and inequality data
have improved
• There is a reduced household burden for the
participation to the survey (the household needs to
spend less time to complete the required information)
• Improvement in the measurement of some key statistics
(remittances and agricultural income)
• Employment data are now collected ensuring
comparability with definitions used in the Labour Force
Survey
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Outline
1. How the HBS changed
2. Assessment of data quality
3. Data comparability
4. Conclusions
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2006 data quality
• Data quality can be assessed looking at internal
data consistency, but also through external
validation
• Internal consistency:
– Relationship between aggregates, prices capturing
inflation, etc.
• External validation:
– Some HBS estimates can be compared to those
provided by other sources
– Such comparisons need to take into account
differences in ways measures are obtained
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Data validation with external
sources
• Demographic indicators: Census
– Composition by age
– Household size
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National income and product accounts
Social protection
Labour Force Survey
Agricultural statistics
Let’s see some examples
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Age distribution – HBS, Census
and demographic statistics
80
HBS 2005
70
HBS 2006
60
Census
50
Demographic
statistics
40
30
20
10
0
0-14
15-64
65+
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Household size
• Average household size, including people working
abroad, is the same in the 2006 HBS and in the Census,
but in previous HBS was considerably lower
• In 2006 distribution of household size is much closer to
that of the Census
Distribution of hh by size
2005 HBS
2006 HBS
Census
30.0
25.0
20.0
15.0
10.0
5.0
0.0
1
2
3
4
5
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Outline
1. How the HBS changed
2. Assessment of data quality
3. Data comparability
4. Conclusions
14
Comparability issues
• The changes described earlier (sampling, questionnaires)
affect the comparability of 2006 estimates with previous
surveys
• It is not possible to compare 2006 with previous estimates
• Let’s make a simple example: Assume that you are
looking at a room from one specific corner
• This room between 1997 and 2007 has changed
considerably
• The perspective that was good in 1997 is no longer
representative now, some parts of the room are no visible
• In 2006 the perspective has changed and all the room
became visible again
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No comparability
• Although the room is the same, we cannot
compare 2005 and 2006 estimates because
2006 data allows us to see part of the room that
were not visible in 2005
• This means that if estimates in 2006 are higher
or lower than those in 2005, we cannot conclude
that estimates have increased or decreased
– For example, if the average household size in 2005
was 2.5 and in 2006 is 3. This does not mean that
households are now larger than before. The part of
the room that we did not see before has clearly an
influence on the new estimate
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Demographic indicators
Household size and type of households
Average hhsize
Single
Couple
Other adults only
Single parent with children
Couple with children
Other hhs with children
2005
2006
2.48
2.79
27.5
20.6
14.7
9.5
19.7
7.9
100.0
20.7
18.5
17.2
7.9
23.0
12.8
100.0
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Example: House types in cities
100%
90%
80%
70%
60%
Private house
50%
Hostels
40%
Apartments
30%
20%
10%
0%
2005
2006
• Detached houses in
2006 are included
in the sample
frame: they
represent 16% of
dwellings.
• In 2005 they
appeared to be unexistent (due to the
old sample frame)
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Example: income and consumption
1000
900
800
700
600
500
400
300
200
100
0
2004
2005
HBS
NIPA
2006
• Both income and
consumption are
now estimated at
much higher
levels than in
2005
• This is in line with
estimates from the
National accounts
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Conclusion
• HBS quality improved substantially and now provides
data that are more representative of Moldova
• Higher data quality means:
– Better understanding of poverty and its characteristics
– Greater ability to inform policy making and monitor policy impact
in the future
• However, 2006 data are not fully comparable with
previous estimates. The degree of incomparability was
somewhat unexpected, but we need to consider that
there was no point in keeping the old design if no longer
fully representative
• To make sure that data remains representative, villages
and enumeration areas will be changed over time and
the sampling frame will also be updated using the
electricity database and making a household listing of
the new selected enumeration areas
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