Transcript PPT

STATISTICAL INSTITUTE OF JAMAICA
Sample Design
Establishments Surveys
Stuart Brown
Research, Design & Evaluation
January 2013
Sampling Frame

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
The Business Register (or Central Register of
Economic Units - CREU)
Does not include agricultural/government
establishments
Contains 7,459 establishments
(as at Jan 24, 2013)
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Establishment Classifications
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Employment size (total number of persons
employed)

Small - less than 10 employees (<10)

Medium – between 10 and 49 employees
(10-49)

Large - 50 or more employees (50+)
Industry

In accordance with Jamaica Industrial
Classification (JIC) 2005
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Common Characteristics
- Sample Design

Single-stage selection

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Only establishments are selected randomly
Stratification by industry, size, geography
Large/Monopoly establishments – all selected
Medium establishments selected randomly

Some medium establishments may be
selected with certainty (i.e. purpose
selection) in special circumstances
Probability Proportional to Size (PPS)
sampling within strata
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Selection Criteria
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Large establishments are selected with certainty
All establishments within industries with six (6) or
less establishments are taken
All establishments which are engaged in specific
activities of interest are taken
PPS sampling method used to take sample from
among medium establishments
 Measure of size: employment size
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Sample Size Formula
2
z pq
n 2
e
n = sample size
z = 95% confidence level
p = population proportion
q= 1-p
e = margin of error
e.g. If z=95%, p=40%, e=3%
Then
n = [(1.96)2 * 0.4 * (1-0.4)] / (0.03)2
= 1024
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Apportioning Groups within Sample
1.
2.
3.
4.
Calculate sample size
Identify groups from which all units will be
selected, and separate from sample and frame
Determine proportions of groups in reduced
frame
Apportion remaining sample according to
proportions in reduced frame
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Sample Allocation
Example:
INDUSTRY
A
B*
FRAME
PROP OF
FRAME1
(%)
PROP OF
FRAME2
(%)
25
13.2
13.5
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2.6
SAMPLE
Calculation
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25/(190-5) x (70-5)
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Select all
C
50
26.3
27.0
17
50/185 x 65
D
110
57.9
59.5
39
110/185 x 65
ALL
190
100.0
100.0
70
Sample (n) = 70
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Response Rates
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Ever declining
 Usually much less than those for household
surveys
Over-sampling done to compensate for expected
non-response
Non-responding establishments not replaced
Out-of-business establishments replaced with
establishments of similar characteristics
Weighting using sampling fractions and nonresponse rates
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END
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