Ryan Braun and Type I vs. Type II Error by Jason Roberts February 24, 2012 I’ll echo Dave Cameron and start by saying I do not know if Ryan Braun cheated. What we do know is that he will not be facing a suspension based on his October 2011 drug test. The independent arbitrator determined that the irregularities in the process were serious enough to warrant tossing out the apparently positive test. It is worth noting that the arbitrator did not declare Braun “innocent,” rather he simply refused to uphold the “guilty” result. In social science terms, the arbitrator decided the risk of making a Type I error was greater than a Type II error. A Type I error occurs when a null hypothesis –- in this case that Braun was clean –- is rejected despite being true. The flipside is a Type II error where a null hypothesis is maintained –- again Braun is clean –- when rejection of the null is warranted. The fact that the arbitrator decided to potentially commit a Type II error is certainly good news for Braun and the Milwaukee Brewers, but is this good for Major League Baseball? I would argue yes. Our society has a long history of preferring Type II errors to Type I errors. The best example is our criminal justice system. Defendants are assumed innocent until proven guilty. A defendant does not have to prove that he or she is innocent of the crime he or she has been charged with, he or she simply has to raise enough reasonable doubt to prevent the state from proving that they did in fact commit the crime. This bias towards Type II errors is often controversial, as there are cases where many people believe that a guilty defendant was freed through the trial process (i.e. e.g. Casey Anthony, O.J. Simpson), but our society still supports a system that attempts to minimize the extent to which innocent individuals are falsely convicted. Regardless of your view of Braun’s culpability it is hard to make a credible argument that MLB should be more accepting of Type I error than the criminal justice system. In the criminal cases cited above we know for a fact that a crime was committed, but the jury was not convinced beyond a reasonable doubt that the accused was the guilty party. The implications of a Type II error in a criminal case are immense, including putting innocent human beings at risk of continued criminal activity by the defendant. In the case of a drug testing controversy, by definition we do not even know for sure that a violation occurred, as such there is less risk that a violation will go unpunished. I would also argue that unlike in a criminal case, making a Type II error in a drug-testing regime does not increase the risk of future policy violations. The fact that this result was overturned does not exclude Braun from the testing program going forward, if anything it may increase the amount of scrutiny he is under. In the criminal justice system, a Type I error can result in an individual spending a portion of his or her life unjustly incarcerated. This loss of freedom has tremendous effects on an individual’s personal life, not to mention the person’s ability to make a living. For an elite professional athlete, the costs of a Type I error are surely less severe than incarceration, but it still represents an unjust shortening of the amount of time they can spend in their profession and an undue stain on their personal and professional reputations. A Type I error hurts the team the player is under contract with, the competitive balance of the league, and it deprives fans of seeing the best athletes playing the game. Some will argue that the Braun case calls into question the integrity of many aspects of the game, including Braun’s N.L. MVP award and the results of the Brewers’ games last year. This is certainly true. However, a suspension of Braun for 2012 was never going to change any results from 2011. If anything I think the ultimate fallout from this case will be positive. Given MLB’s reaction to the decision it seems likely that changes will be made to the testing regime in the wake of this case that will hopefully further minimize the probability of both Type I and Type II errors in the future, a result that MLB, the players, and fans alike should be rooting for.