Detailed Instructions: In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Q: If two variates obey this, their difference obeys a Skellam distribution. It has moment-generating function e to the quantity lambda times quantity e to the t minus one, where lambda is the only parameter on which this distribution depends. Bortkiewicz called it the "law of small numbers" after noting that it models rates of rare events like radioactive decays or horse-kick deaths. This function gives as lambda to the n times e to the minus lambda over n factorial as the probability of n successes from a large number of the trials named for its French namesake. FTP, name this distribution usually symbolized P.
A:
Science