As a sporting federation recognized by the IOC, and particularly as a signatory to the World Anti-Doping Agency (WADA) conventions, FIDE adheres to their rules, including a requirement for doping tests, which they are obligated to take at the events such as the Olympiad. The tests were first introduced in 2002 under significant controversy, with the widespread belief that it was impossible to dope in chess. Research carried out by the Dutch chess federation failed to find a single performance-enhancing substance for chess. According to Dr Helmut Pfleger, who has been conducting experiments in the field for around twenty years, "Both mentally stimulating and mentally calming medication have too many negative side effects". Players such as Artur Yusupov, Jan Timman and Robert Hübner either refused to play for their national team or to participate in events such as the Chess Olympiad where drug tests were administered. All 802 tests administered at the 2002 Olympiad came back negative. However, in the 36th Chess Olympiad in 2004, two players refused to provide urine samples and had their scores cancelled. Four years later, Vassily Ivanchuk was not penalized for skipping a drug test at the 38th Chess Olympiad in 2008, with a procedural error being indicated instead.