Sample Design

Establishments Surveys

Stuart BrownResearch, Design & EvaluationJanuary 2013

STATISTICAL INSTITUTE OF JAMAICA

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Sampling Frame

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

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 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

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

n = sample sizez = 95% confidence levelp = population proportionq = 1 - pe = margin of error

e.g. If z=95%, p=40%, e=3%Thenn = [(1.96)2 * 0.4 * (1-0.4)] / (0.03)2 = 1024

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2

e

pqzn

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Apportioning Groups within Sample

1. Calculate sample size2. Identify groups from which all units will be

selected, and separate from sample and frame3. Determine proportions of groups in reduced

frame4. Apportion remaining sample according to

proportions in reduced frame

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Sample Allocation

Example:

INDUSTRY FRAME PROP OF FRAME1 (%)

PROP OF FRAME2 (%)

SAMPLE Calculation

A 25 13.2 13.5 9 25/(190-5) x (70-5)

B* 5 2.6 5 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

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 non-

response rates

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END