Transcript Finding and Identifying 15 year olds

2B. Finding and identifying:
Sampling
Sampling within an Identified Area
• Directly drawing a sample of OOS 15 year olds
probably not very sensible because a ‘listing’
has to include two further sets of questions:
• (a) to confirm that the teenager really is 15
• (b) to establish the 15 yo’s exact school status
• These would require presence of 15 year old
which cannot be guaranteed
• Probably better to first identify ALL households
reporting a 15 yo in the household
• Make an appointment to return when 15 yo
will be asked to be there
Deriving a Random Probability Sample
• Divide country into administrative (provincial
or regional) units, and usually also into urban
and rural areas to create strata
• Within each stratum, census or enumeration
areas (EAs) - or each selected segment of an
EA if the EAs are too large - are selected with
probability proportional to size,
• Households within each selected EA or
segment of an EA are listed together with the
ages of household members;
• Households reporting a 15 year old are the
sample to be interviewed.
Problem with Cluster Sampling
• Classic sampling designs of DHS/MICS are
based on cluster sampling points, the areas
selected with probability proportional to size
• The selected areas are then relisted but the
disparity in size do not seem to be taken in
account when calculating sampling errors
Rarity of OOS
• A mock calculation suggests that, if a sample
size of OOS 15 year olds is required to be
proportional to the typical PISA in-school
sample size of 5,000, then we need a target
population of 2,100. Given the rarity of 15
year olds and that OOS are about a third of
those, then we need an initial listing of 63,000
households. The costs would be prohibitive
• It helps that PISA requires a minimum of only
150 schools in the sample although that
would mean only sampling 14 per point
Options for Reducing Costs
Option 1: Starting from Strand A school areas
• Choosing fewer sampling points. The costs
would decrease proportionately but the
Design Effects would increase
• Choosing fewer respondents within each
sampling point so decreasing the Design Effect
but not substantially reducing the cost
Options for Reducing Costs
Option 2: Targeting specific areas
• Purposefully target specific areas either
through local knowledge about rates of
enrolment, or with poverty maps, or specific
targeting of vulnerable groups
– 2A: Direct approaches: Households
– 2B: Indirect approaches: Employers, Marginal
groups in urban areas
Option 2:
Targeting Specific Areas
• If targeting is adopted, selection of areas
should be oriented towards the likelihood of
finding OOS 15 year olds
• Given wide variation in country contexts, it is
suggested that country teams include
someone who can contribute to defining a
poverty map
• Sample in rural areas
Direct Approaches
Rural Areas
• In small towns, villages, possibly use local
informants; if not re-list households a la DHS/
MICS, noting age of each household member
• Where there are substantial numbers of
nomadic/pastoralists, there are recognised
procedures for sampling
Urban Areas
• List households in specified areas, possibly with
citizen volunteers (ASER and UWEZO)
• Could be difficult where parents are concerned
about security of children
• In slum areas, could be difficult to list households
Indirect Approach
• Search for working 15 year olds in formal
employment
• In participating countries, most males report
that they are working, whilst much wider
variation for females; but percentages working
for someone outside household are much
lower; and, apart from females living in urban
areas in Cambodia and Guatemala, always
lower than 20%
Sampling from Employers
• First compile a list of all businesses working in
the area together with their telephone
numbers
• Second, ring up their personnel departments
(if they have one) to find out their size and
whether or not they have any teenagers
working for them
• Third, if there are a sufficient number of such
businesses, divide the reduced list of
businesses into small, (medium), and large
enterprises and sample from them
proportional to size.
Marginal Groups in Urban Areas
• Non-household populations
• Methods have been developed to estimate
numbers of street children in several places
• Internally Displaced Persons
• They will be reluctant to take part in any
semi-official exercise
Questions for discussion
• How to survey out of school 15 year olds?
• Advantages and disadvantages of option 1 and 2?
• Are these options mutually exclusive or
complementary?
• Can you think of other options?
• What are the costs implications?
• How about synergies with other Strands?
• What is an appropriate ambition for PISA-D?