Mathematical statistics, if viewed as a branch of mathematics, is motivated partly by its own internal structures and aesthetics. Statistical science in general, however, is driven primarily by problems arising in applications. One might in fact define statistics in general as the science of answering questions formulated in other disciplines. New statistical tools are developed to answer new problems arising in the areas to which statistics is applied, as well as to answer old problems more accurately. The ability to give better answers to old problems occurs as restrictive and unrealistic assumptions are relaxed, so enabling more appropriate models to be constructed and fitted to the data. Such models arise as a result of progress in theoretical statistics and advances in computer technology.