on behalf of the American Thoracic Society/ European Respiratory Society Working Group on Infant and Young Children Pulmonary Function Testing This official statement of the American Thoracic Society (ATS) and the European Respiratory Society (ERS) was approved by the ATS Board of Directors, September 2006, and the ERS Executive Committee, December 2006 6. Further multidisciplinary work is required to investigate the best combination of tests (e.g., structure, function, inflammation, atopy) and challenges (e.g., pharmaceutical vs. physical) to investigate specific clinical entities during early childhood.

SUMMARY When a study produces estimates for many units or categories a common problem is that end‐users will wish to make their own comparisons among a subset of these units. This problem will occur, for example, when estimates of school performance are produced for all schools. The paper proposes a procedure, based on the graphical presentation of confidence intervals, which enables such comparisons to be carried out while maintaining an average required type I error rate.

The analysis of repeated measures data can be conducted efficiently using a two-level random coefficients model. A standard assumption is that the within-individual (level 1) residuals are uncorrelated. In some cases, especially where measurements are made close together in time, this may not be reasonable and this additional correlation structure should also be modelled. A time series model for such data is proposed which consists of a standard multilevel model for repeated measures data augmented by an autocorrelation model for the level 1 residuals. First- and second-order autoregressive models are considered in detail, together with a seasonal component. Both discrete and continuous time are considered and it is shown how the autocorrelation parameters can themselves be structured in terms of further explanatory variables. The models are fitted to a data set consisting of repeated height measurements on children.

A method is described for calculating age-related centiles which makes no assumption about the nature of the distribution of the measurement at a fixed age.