BERLIN A study by U.S. and German universities found unusual betting patterns at some Bundesliga matches between 2010 and 2015 when three particular referees were involved, WDR TV said on Friday.
The study, by Bielefeld University and the universities of Pennsylvania and West Virginia, involved bets placed through on-line betting company Betfair on 1,252 matches from 2010 to 2015.
The report's authors said that the patterns were unusual in some cases but match manipulation could not be proven.
The German football association (DFB) responded by saying there had been no suspicion of manipulation in any Bundesliga matches for more than a decade.
Germany's biggest betting scandal was in 2005 when referee Robert Hoyzer was jailed for match fixing in a two million euro ($2 million) betting fraud that caused huge embarrassment to the host nation of the 2006 World Cup.
Hoyzer admitted to fixing games for a betting ring and later fully cooperated with authorities.
The DFB said in its statement that since then it and the German football league (DFL) had been working with monitoring specialists Sportradar to identify betting abnormalities.
"Since then (2005), no game in the Bundesliga or Second Bundesliga have been rated as suspected of manipulation by Sportradar," it said.
(Reporting by Karolos Grohmann; Editing by Louise Ireland)