In many surveys, including the Current Population Survey of the U.S. Bureau of the Census and the Labour Force Survey of Statistics Canada, participants are interviewed a number of times during the life of the survey, a practice referred to as a rotation design or repeated sampling. Often composite estimation--where data from the current and earlier periods of time are combined--is used to measure the level of a characteristic of interest. As other authors have observed, composite estimation can be used in a rotation design to decrease the variance of estimators of change in level. We derive simple expressions for the variance of a general class of composite estimators for level, average level over time, and change in level. These formulae hold under a wide range of rotation designs.