Of the companies revising their current budgets, 27% made increases and 22% made decreases.
Of the companies setting new budgets, a net 20% made increases compared with their actual marketing spend in the first quarter of 2004.
This was the weakest improvement for three years and a sudden deceleration from the net 38% of companies that increased their new budgets in the last quarterly report.
Money allocated to traditional media advertising and sales promotion was reduced in new and revised budgets, while direct and digital marketing budgets were raised.
According to IPA president Stephen Woodford, media budgets are the most sensitive barometer of marketing people's views on consumer confidence.
Woodford said: "Uncertainty about consumer spending, higher interest rates and the housing market may be causing some companies and sectors to be more cautious about the coming year, until they can see the lie of the land."
The report's author, Chris Williamson of NTC Research, said: "Total spend for 2005 remains set to exceed that of 2004. However, we may yet see companies revise down their marketing spend for the year, particularly for higher-cost media activities, if oil prices remain high and economic growth in key markets such as the euro area remains lacklustre."
Sir Martin Sorrell, chief executive of WPP, said: "Clearly, clients are looking for new media and technology alternatives [to traditional media]."
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