Mixed-e?ects models provide a ?exibleand powerful toolfor theanalysis of grouped data, which arise in many areas as diverse as agriculture, biology, economics, manufacturing, and geophysics. Examples of grouped data - clude longitudinal data, repeatedmeasures, blocked designs, and multilevel data. The increasing popularity of mixed-e?ects models is explained by the ?exibility they o?er in modeling the within-group correlation often present in grouped data, by the handling of balanced and unbalanced data in a uni?ed framework, and by the availability of reliable and e?cient software for ?tting...