IOS supplementary information

Supplementary information for the Index of Services.

The experimental Index of Services (IOS) was first published in Northern Ireland on 18 May 2005. Following assessment by the UK Statistics Authority the IOS was designated as a National Statistics on 5 August 2011.

Overview of the Northern Ireland Index of Services

The IOS is published quarterly and is designed to provide a general measure of changes in the output of the private sector service industries in Northern Ireland. This is defined as Standard Industrial Classification 2007 (SIC07) sections G to S.  Based on employee jobs, in 2014 these private sector service industries accounted for 61% of regional Gross Value Added (GVA).

The quarterly NI IOS Statistics Bulletin presents the latest seasonally adjusted estimates from the NI Index of Services including comparison with published figures for the UK as a whole.

The IOS sample was refreshed and boosted during Quarter 1 2014 to approximately 3,500 companies. Prior to this period, there were approximately 1,900 following a sample refresh in Quarter 2 2011. The sample of service 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 economy whilst ensuring burden on businesses is kept to a minimum.

The census element consists of all companies employing 100 or more employees and those employing 0 to 99 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 IOS is based on up-to-date information about the output and sales of the services 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 now over 80 per cent.

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.  Deflators adjust the value series to take out the effect of price change to give the volume series. 

Since the beginning of 2016, data is now collected from the combined Quarterly Business Survey. Prior to this, businesses received an Index of Services form and/or a Quarterly Employment Survey form. Companies are now asked to provide employment and 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 receiving two separate forms at different times.

ONS deflation methodology

Further information