The use of the much-debated Decision Review System (DRS) in the World Cup has improved the incidence of correct decisions by five per cent, ICC chief executive Haroon Lorgat told reporters at a press conference in Ahmedabad on Wednesday.Lorgat also backed the decision of the World Cup organisers to hold the summit clash of cricket's showpiece event at Mumbai's Wankhede Stadium which has a smaller capacity than some other grounds in India.But he rubbished the reports that the World Cup round-robin match between Australia and Zimbabwe was under investigation for match-fixing and described the claims as 'fictional'.The 'Times of India' recently carried a report saying the above-mentioned match on February 21 was under ICCinvestigation for match-fixing, and the ICC has now asked the newspaper to either substantiate its claims of corruption or issue immediate retraction.