  Can one understand the statistics of wins and losses of baseball teams? Are
their consecutive-game winning and losing streaks self-reinforcing or can they
be described statistically? We apply the Bradley-Terry model, which
incorporates the heterogeneity of team strengths in a minimalist way, to answer
these questions. Excellent agreement is found between the predictions of the
Bradley-Terry model and the rank dependence of the average number team wins and
losses in major-league baseball over the past century when the distribution of
team strengths is taken to be uniformly distributed over a finite range. Using
this uniform strength distribution, we also find very good agreement between
model predictions and the observed distribution of consecutive-game team
winning and losing streaks over the last half-century; however, the agreement
is less good for the previous half-century. The behavior of the last
half-century supports the hypothesis that long streaks are primarily
statistical in origin with little self-reinforcing component. The data further
show that the past half-century of baseball has been more competitive than the
preceding half-century.

Physics and Society;Data Analysis, Statistics and Probability