HOW THE TOP 100 IS COMPILED

The Top 100 lists are compiled by Nielsen from the billing and account information provided by agencies. To be included in the listings, agencies must have sufficient billings on above-the-line advertising in the UK and advise of any client wins and losses for the current year.

Nielsen compiles the agency client assignments from data supplied by agencies and media owners on a regular basis and from published announcements. It does not include actual billings or agency revenues. The figures represent estimated costs of buying media space based on a number of factors, including ratecard, discounts and viewing figures. Press expenditures include an Advertising Association discount factor, which varies according to the sector and quarter.

Media measured includes television, display press, radio, cinema, out-of-home (booked via outdoor specialists but not including ambient, international sites or point-of-sales), online digital display, mobile and video advertising. Direct marketing, such as direct mail, is not included, reflected in the low billings for most of the DM agencies featured.

Any reference to the 2015 rankings is based on the most up-to-date information available. This may differ from the original published data as changes such as Nielsen product enhancements with back data, industry mergers, billings or agencies that have ceased trading are included.

The objective representation of the dynamic agency market is crucial.

All data is rigorously reviewed and analysed to ensure an accurate reflection of the data provided.