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This document outlines the sample design used by the Statistical Institute of Jamaica for establishment surveys, detailing the sampling frame, classifications, common characteristics, selection criteria, sample size formula, and allocation methods. It also discusses response rates and weighting techniques.
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STATISTICAL INSTITUTE OF JAMAICA Sample Design Establishments Surveys Stuart Brown Research, Design & Evaluation January 2013
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)
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
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
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
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% Then n = [(1.96)2 * 0.4 * (1-0.4)] / (0.03)2 = 1024
Apportioning Groups within Sample • 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
Sample Allocation Example:
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