Australian business confidence improved in September but remains subdued, according to a business survey released on Tuesday by National Australia Bank (NAB). The latest NAB Monthly Business Survey showed the business confidence index, a key barometer of sentiment in the business, rose to zero in September from minus three points in August. NAB said in a statement on Tuesday that major stimulus announcement by the U.S. Federal Reserve (Fed) and the European Central Bank (ECB) had helped lift Australian business confidence. However, NAB said, confidence remained well below its long-term average, due to ongoing concerns about the value of the Australian dollar and falling commodity prices. "Confidence is now six points below the long-run average and has been subdued relative to the average for more than a year," NAB said. The NAB business survey also found the business conditions index fell to minus three points in September, down from zero the month before and well below the long run average of one. The bank said declines was broad-based, with heavy falls for wholesale, retail and transport, and utilities in the month.