Nomura has reduced its target price for advertising and media giant WPP from 1,030p to 980p after cutting its forecasts for organic growth on the back of a slowing macro-economic environment.In a research report published late on Thursday, the broker said it has slashed its organic growth estimate for 2013 from 2.5% to just 1%, "demonstrating further that momentum has changed for the company and the sub-sector".The broker said: "This could appear harsh, but the range of outcomes has seriously widened given zero growth in September 2012."Good arguments could be made for 3% growth in 2013 (easy comps, US fiscal cliff avoided, Europe stabilised and a soft landing in China), or for -4/5% (US fiscal cliff becomes real, the euro heads towards a break-up and China has a hard landing)."Nomura has reduced its 2012 and 2013 earnings per share (EPS) forecasts by 1.7% and 4.3%, respectively. While revenue estimates are also reduced, the broker still forecasts a 3.5% increase in revenue in 2014 driven by "hoped-for economic improvement, the World Cup in Brazil and US elections."Despite the reduction in target price, Nomura says that while momentum for the whole agency sub-sector is poor, the valuation - shares trade at 10.6 times earnings - is relatively low. A 'buy' rating is retained.BC