IOP supplementary information

Supplementary information for the Index of Production.


Overview of the Northern Ireland Index of Production (IOP)

The Index of Production (IOP) is published quarterly and is designed to provide a general measure of changes in the output of the manufacturing, electricity, gas, water and mining and quarrying industries. This is defined as Standard Industrial Classification (SIC) 2007 sections B, C, D and E. In 2014 these industries accounted for approximately 18% of regional Gross Value Added (GVA). The IOP is one of the earliest official indicators of the performance of the NI production sector and represents an important short term measure of change in this area of the economy.

The quarterly IOP provides information on the output of the production industries, manufacturing industries, manufacturing productivity and market trends. For the production industries equivalent UK figures are provided for comparison.

The IOP sample was refreshed for Quarter 1 2014 and was drawn on a SIC07 basis. The sample was boosted from around 650 businesses and it is now approximately 1,100 companies. The sample of production industries is selected directly from the Inter Departmental Business Register (IDBR), by stratifying companies by industry and company size. The sample consists of a census of dominant companies and a Neyman stratified random sample of the remaining medium and smaller businesses, which are normally selected on a rotational basis. The sample has been designed to give sufficiently accurate results on the performance of the NI production sector whilst ensuring burden on businesses is kept to a minimum.

The census element consists of all companies employing 40 or more employees and those employing 0 to 39 employees and having a turnover of £10 million or more. It is desirable to include these low employment high turnover companies in the sample in order to provide a more comprehensive picture of the overall economy.

The IOP is based on up-to-date information about the output and sales of the production industry. The index is published in March, June, September and December each year and refers to the quarter ending some 11 weeks earlier. As a statutory survey the response rate is around 80%.

All series are measured at constant market price (2019 = 100) and are seasonally adjusted using X-13 ARIMA SEATS in order to obtain a clear picture of the general trend. For practically all series, the value of sales is deflated to remove the effect of price change.

Since the beginning of 2016, a Quarterly Business Survey form was issued to all businesses who previously received an Index of Production form and/or a Quarterly Employment Survey form and companies are now asked to provide employment and/or turnover information at the same time. This combined survey form, coupled with the roll-out of an ‘eForm’ (designed to collect data electronically) is intended to reduce the burden to businesses currently receiving two separate forms at different times.

Methodology and summary of uses

National statistics

Following assessment by the UK Statistics Authority, the IOP was reaccredited as a National Statistic on 5 August 2011.

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