NEW YORK: Digital now accounts for a quarter of all expenditure on media by leading US agency holding companies, new figures show.

Standard Media Index, an independent source of advertising expenditure data, released publically for the first time aggregate figures compiled directly from data processing systems used by major holding groups like Aegis, Havas, Interpublic and Publicis in the US.

These showed media spending on television gradually slowing while that on digital rises at a faster rate.

"Television spend continues to slow - at a rate of -2% during the first quarter of 2013 - driven by March's year-over-year decline of 5%," SMI analyst Kristina Luland told MediaPost.

The equivalent year-over-year increase for digital was 15%. During the first quarter of 2013, digital spending rose 17% to account for 23.5% of agency media buys. In March that figure hit 24.6%, while television's share was down to 60.3%.

While not directly comparable, Warc's latest International Ad Forecast predicts that digital spending will make up 25.6% of total US adspend during 2013.

The fastest growing digital sectors during the first quarter, according to SMI, were mobile, up 92%, and exchange-based digital buys, up 46%.

Display and search, however, still accounted for the greater part of digital spending and rose at slower rates, both up 12%.

Direct-from-publisher display advertising accounted for 8.6%, and search accounted for 6.2% of all buys made by the major agencies.

In another development, SMI's data show that cable network spending during the first quarter accounted for a greater share of agency budgets than the major broadcast networks.

Data sourced from MediaPost; additional content by Warc staff