Sample Design Establishments Surveys Stuart Brown Research, Design & Evaluation January 2013 STATISTICAL INSTITUTE OF JAMAICA

2 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)

3 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

4 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

5 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

6 Sample Size Formula 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

7 Apportioning Groups within Sample 1. Calculate sample size 2. Identify groups from which all units will be selected, and separate from sample and frame 3. Determine proportions of groups in reduced frame 4. Apportion remaining sample according to proportions in reduced frame

8 Sample Allocation Example: INDUSTRYFRAME PROP OF FRAME1 (%) PROP OF FRAME2 (%) SAMPLE Calculation A /(190-5) x (70-5) B* Select all C /185 x 65 D /185 x 65 ALL Sample (n) = 70

9 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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