Sentiment among German analysts and institutional investors further deteriorated in December to the lowest level in over 15 years, a survey from the Center for European Economic Research showed Tuesday. The think-tank's economic expectations index hit the lowest level since January 1993, amid fears of a sharp slowdown in U.S. economic growth and a strong euro, falling to -37.2 points in December from -32.5 points in November. That was below economists' forecasts of -34.0 points, and well below the indicators' historical average of 31.4 points. "The financial market experts see clear risks for economic growth in important industrial countries, particularly in the U.S. This impairs the export prospects of the German economy," ZEW said. The strong euro is also a concern, particularly as survey participants don't envisage a pickup in consumer spending, the survey showed. The 284 analysts and institutional investors polled in December also assessed current economic conditions less favorably. The corresponding indicator fell to 63.5 points, after being broadly stable at 70.0 points in November, the survey showed. "The German ZEW business expectations data look seriously weak and sound an early warning signal to a deeper downturn ahead in Germany and the euro zone," said David Brown, Chief European Economist at Bear Stearns. ZEW President Wolfgang Franz defended the European Central Bank's policy stance. The ECB was "totally right" in keeping the key policy rate unchanged at 4.0% at the Dec. 6 rate-setting meeting, but it should raise rates again, if financial markets calm down, he said.