Transcript Frames for agricultural census and surveys

FRAMES FOR
AGRICULTURAL CENSUS
AND SURVEYS
INTRODUCTION
 The Samoan households survey framework
incorporates the following sampling
schemes
‫ ٭‬Stratified sampling.
‫ ٭‬Two Stage sampling
‫ ٭‬Probability Proportional to Size sampling
‫ ٭‬Systematic sampling
Stratified Sampling
 The Stratum adopted for the survey are
the 4 Statistical Regions which make up
Samoa
‫ ٭‬Apia Urban Area
‫ ٭‬North West Upolu
‫ ٭‬Rest of Upolu
‫ ٭‬Savaii
Two Stage Sampling
 The two stages of the survey are as follows
Stage 1
Selection of enumeration areas
Stage 2
Selection of households within the selected
enumeration areas
Probability Proportional to
Size Sampling
 For the first stage the EA’s are selected
based on their size
 The size measure is the number of h/h’s
in EA according to the frame
 An EA with 100h/h’s will therefore have
as much chance of selection as an EA
with 50h/h’s
Systematic Sampling
 The second stage of selection, the
households are selected using
Systematic skip
The Cluster Size
 An early question to address in setting up the
Framework is to determining how many
households do we need to select per selected
EA
 This is commonly referred to as the cluster size
 This is generally determined at the stratum
level
The Cluster Size (cont)
 For Samoa, no technical work was undertaken
to determine the most optimal cluster size.
 Instead we plagiarized results from other
countries
 This resulted in a cluster size for each region of
AUA – 5
NWU – 10
ROU – 10
SAVAII - 10
How many H/hs do we
Select ?
Best illustrated via an example (AUA) only
● Say we desire a 10% sample
● Total H/hs in AUA = 5182 (census06)
● This mean for AUA, we need a Sample size
of (10/100)*5182=518 h/hs
Selecting the Villages and EAs
Step1
Order villages by their geographical location within
each Region
Step 2
Attach the total EAs for each village as well as the
the total households for each EAs
Step 3
Convert the count of h/hs to the number of clusters by
dividing the total h/h by cluster size for each Region. Eg
(AUA=5)
Step 4
Calculate the Cumulative number of clusters and add to
the list for each Region
Selecting the Villages and EAs (cont)
Step 5
Determine the skip to be run through the list for each Region
=(total #clusters in each region)/(selections for the region)
Step 6
Select a Random Start between the value of the skip and 0
Step 7
Produce the remaining selections numbers by continuously
adding the Skip to the random start until you reach the total
number of clusters in the stratum
Step 8
To determine the selected villages, locate the village with
the lowest cumulative # clusters value which is higher than
the selection number
Note: At the same time the EAs is also selected
(NB: there may be 2 or more selections from village)
Selecting the Households
 On the household list of the selected village and
EAs assign a cluster number to each h/h
according to the Cluster Size
 Continue until the number of the clusters has
been reach and then start at 1 again and repeat
the process
Selecting the Cluster
 To determined which h/h or cluster to be
selected, Subtract the selection number from
the previous Cumulative number.
 Household list
For Excel file
1999 Census of
Agriculture Framework
FAAFETAI LAVA !!!