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2. Population sources Sampling process – Sample design – Sample selection – Proving 2

3. 3 FDI population consists of three sources which are combined into one population: World-based extract Dun & Bradstreet external administrative data Inter-departmental Business Register (IDBR) comprehensive list of UK businesses and provides the main sampling frame for business surveys FDI/Non-World-based CORA Sample previous sample

4. Is an American public company headquartered in New Jersey. They provide commercial data to businesses on credit history, sales and marketing, company structures, foreign links and many more. A major source of information that is used to keep the IDBR up to date. 4

5. 5 Introduced in 1994 and is a comprehensive list of UK businesses that is used by government for statistical purposes The two main update sources for IDBR are VAT and PAYE It provides the main sampling frame for surveys of businesses carried out by the ONS and by other government departments. It is also a key data source for analyses of business activity The IDBR covers over 2.1 million businesses in all sectors of the UK economy, other than some very small businesses (those without employees, and with turnover below the tax threshold) and some non- profit making organisations

6. 6 Information from previous year’s sample is used to update the new population Update company’s information – Industry – Net Book value – Affiliate data – Source information

7. 7 WB N = 26,000 FDI N = 21,000 Sample

8. 8 D&B IDBR WB Duplicates WB CORA WB Sample design Final population Dun & Bradstreet information Worldbase extract Information held on CORA Worldbase sample CORA sample IDBR information Final selection Worldbase Strand CORA Strand Worldbase & CORA mixed Sample design Sample prove

9. 9 Methodology provide optimal sample design and allocation for both annual and quarterly surveys Quarterly sample is a subset of annual sample Population and sample are updated for Quarter 1 each year Once sample is selected, it is then cleaned to remove duplicates and ensure contact details area up to date

10. 10 Stratify by industry and sizeband (NBV, turnover or number of affiliates depending on survey) Fully enumerate top size bands as these are main contributors Random sample of smaller businesses Our FDI sample represents the whole economy excluding the banking sectors (Banks, Property and Bank Holding Companies) – These are collected and supplied to us by The Bank of England

11. 11 PRN – Permanent Random Number Allocated at random to each RU at time of birth 9 digits long: between 0 and 1, e.g. 0.123456789 Sampling Arrange all RUs within a cell in numerical order of PRN Specify a PRN start (s), and a sample size (n) Start from s and work along the line, selecting the first n units

12. 12 N (population size) = 10 n (sample size) = 5 s (start point) = 0.5 The 10 units have PRNs: 1 0.396283811 2 0.661458605 3 0.228230336 4 0.308116984 5 0.973739618 6 0.084284942 7 0.844605739 8 0.548379318 9 0.193395484 10 0.493430615 and arranged in PRN order: 6 0.084284942 9 0.193395484 3 0.228230336 4 0.308116984 1 0.396283811 10 0.493430615 8 0.548379318 2 0.661458605 7 0.844605739 5 0.973739618

13. A convenient way of visualising the ordered units is to mark the points on a line – we call this the PRN line Unit 6 9 3 4 1 10 8 2 7 5 |-------------------------------------|-------------------------------------| PRN00.5 1 The interval from 0.5 to the end of the sampled units is known as the sampling interval s

14. We rotate the sample from period-to-period – dropping some of the businesses and gaining some others. We deliberately leave some businesses in the sample for the next period – those in common help to give stability to our surveys. For FDI sample is fixed for 4 quarters then 50% of sample is rotated before Q1.

15. We already have the first sample of n units. Then calculate the number of units to drop in the next sample period using the formula: Number of units to drop = n / r Set the PRN start point for the next period (s 2 ) to be immediately after the last business to be dropped. So … count along the first n / r units (the ones to be dropped next time) to determine the new PRN start point.

16. Example - Rotate out n / r units. Here, this will be 5 / 5 = 1 unit. The unit to be dropped is from the leftmost end of the sampling interval (unit 8 with PRN 0.548379318) PRN start is recalculated as 0.548379319 The sample for period 2 is units 2, 7, 5, 6 and 9. Unit 6 9 3 4 1 10 8 2 7 5 |-------------------------------------|------------------------------- PRN 00.5 1 S2S2

17. 17 Load on IDBR Forms printed / SEFT questionnaire despatch SEFT / paper despatched to respondent

18. 18 Questions?