Chess Olympiad 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. In 2010, a FIDE official commented that due to the work of the FIDE Medical Commission, the tests were now considered routine. In November 2015, FIDE president Kirsan Ilyumzhinov announced they are working with WADA to define and
Return period interest and formula_5 is the counting rate. If the return period of occurrence is 1 in 234 years (formula_5 = 0.0043) then the probability of no occurrence in ten years is In a given period of "n" years, the probability of a given number "r" of events of a return period formula_5 is given by the binomial distribution as follows. In the limit of :formula_11, such that formula_12 then Take where Given that the return period of an event is 100 years, So the probability that such an event occurs "exactly once" in 10 successive years is: Return period is