Information - How The Index Works

The born Job Advertising Index is calculated by measuring the change in job advertising volumes on a selection of UK based job boards. The following explains how we reach the index value.

Phase One: Base Values

Before a job board is included in the index we monitor the average number of job advertisements that appear on the board for a one month period.

This value is then set as the job board's base value, i.e. the value against which all subsequent months are measured.

This does, of course, introduce some issues. For example if the base value is taken when the job board is experiencing particularly high or low advertising volumes, subsequent comparisions against that month can be effected.

However, given the pace at which new job boards are coming to market, the index's use of weightings and the manner that the index is calculated, we believe this method for ascertaining base values is appropriate.

Phase Two: Monthly Values

Over the course of each calendar month, we record the average number of job advertisements that appear on a job board.

The source of this figure typically comes from the job boards themselves, most job boards display the number of adverts they are currently carrying.

In instances where the job board does not openly state it's job advertisement count, or if a job board has experienced technical difficulties during the month, we use a number of proven methods to obtain a figure, with an accuracy of ±2%.

We are currently recording figures for 118 UK job boards.

Phase Three: Calculating The % Change

At the end of each month, we analyse the figures for each job board and establish the % change that has occurred between the current month and the base value.

For example, if a job board had on average 2,000 job vacancies advertised in it's base month and 2,200 vacancies in August, the % change would be 10%.

This is an important aspect of the index; it is a measure of change, rather than a direct measure of volume, although the two are clearly linked.

Phase Four: Establishing Weightings

The next step in the process is to establish figures called weightings.

To do this, we total up all of the average number of job advertisements for the current month, to get the total advertisement count.

The weighting is the percentage of the total advertisement count that each board's average number of job advertisements accounts for. This figure provides an indication of each job board's advertisement share, in the context of the monitored boards, for the current month.

For example, if the total advertisement count was 500,000 and a job board's average number of job advertisements was 50,000, the job board's weighting value would be 10%.

The weighting figure helps to put each job board's % change value into context. It provides the index with resilience and consistency, even when new job boards are added or if a job board's figures are removed or excluded for a period.

Phase Five: Calculating The Weighted % Change

The fifth step in the process is to take each of the % change values and multiply them by the associated weighting value. The outcomes are totalled and then divided by the number of job boards being monitored. This results in a total weighted % change value.

Phase Sixth: The New Index Value

Finally, the index's base value (100) is multiplied by the total weighted % change value, to give us the new index figure.