Seasonal adjustment of the Vacancy Survey data

Labour Market Trends, Dec 2004 by Treasure, Helen

The seasonal adjustment is of an acceptable quality for the monthly and rolling quarterly totals, all size bands and all broad industry groups except for the two industry series which are not adjusted.

Constraining the series

The five vacancies by size series are scaled to sum to the seasonally adjusted (quarterly) total series. The vacancies by industry series are scaled in a similar way, except for the two series that are not seasonally adjusted, which are excluded from the scaling. The remaining six industry series are scaled to the Vacancy Survey total minus energy and water and other services. The results by size and industry are therefore consistent with the seasonally adjusted quarterly totals. The scaling does not have any significant distorting effects on any of the series.

Revisions policy

Each month, the unadjusted data are revised back three months to take account of late information on vacancies or amendments to previous returns in the survey. Similarly, each month the seasonally adjusted data will also be revised back three months. In addition, the data point for the corresponding month or quarter a year ago will also be revised. This is because the series are short, and new data points can significantly change the estimate of the seasonal factors, affecting the seasonally adjusted figure for a year ago.

Recent results and trends

Figures 1 and 2 show the unadjusted and seasonally adjusted totals (monthly estimates and three-month rolling averages). Figures 3 and 4 show the results by size and industry. The results show an increasing trend in vacancies since mid-2003. The increase has been strongest in the finance and business services sector, but there have also been recent increases in education, health and public administration, hotels and restaurants, and manufacturing. The increases have been most pronounced for the largest companies, employing over 2,500 people, for which there has been a rising trend for much of the period since the end of 2001. The smallest businesses have shown a decline in vacancies in the period since AprilJune 2001 but a rising trend since mid-2003.

Available series

The seasonally adjusted series are available starting from April-June 2001. The total seasonally adjusted series and the series by broad industry group are now being published in the monthly labour market statistics First Release (Tables 21 and 22). All the results will be included in Tables G.1 to G.4 in the Tables section of Labour Market Trends from December 2004. All the available data from the survey, both seasonally adjusted and unadjusted, are also available on the National Statistics website.

Further information

For further information, contact:

Andrew Machin,

Room B2/03,

Office for National Statistics,

1 Drummond Gate,

London SW1V 2QQ,

E-mail: andrew.machin@ons.gov.uk, Tel: 020 7533 6162.

Box 1

Seasonal adjustment using X-12

Seasonal adjustment is the process of identifying and removing the seasonal component from a series leaving the trend and irregular components.