Determination of the population size in an epidemiological study with children

Objectives: To obtain a reliable estimate of the population size in an epidemiological study concerned with incidence estimation. Methods: In the present case, the population of interest consists of all children attending a certain pediatric practice for any reason and is estimated making use of the number of regularly attended well baby visits. In some cases, exact figures from the practices are available as a reference. A prospective epidemiological study on the estimation of the incidence of lower respiratory tract infections (LRTI) in the German pediatric population (PRI.DE, Parainfluenza- und Respiratory-Syncytial-Virus-Infektionen in Deutschland) is used to demonstrate the procedure. Results: In most cases, the fit can be regarded as good with deviations between 11% and 17%, whereas in a few cases it must be considered as poor (deviations of 60%). Conclusions: The importance of using exact figures whenever obtainable and of appraising the results carefully is emphasized.