The primary goal of business panels is to obtain estimates of the turnover, including estimates of the changes of the level of the turnover. Panels can also be used for obtaining observations on prices of goods or services for the producer price index (PPI) or the price index for services (SPI). The present document pays special attention to the variance of the estimator of a change of the level of the study variable in a given period. Complicating factors in a panel as panel attrition; births and deaths; and the fact that enterprises may migrate between strata are taken into account. The consequences of combining or splitting up enterprises are discussed as well. Due to the specific variance analysis of the estimates thus obtained, the document has a rather technical character.