Changes in data collection and storage will also lead to new research directions. For example, in the past, panel data (called longitudinal data in biostatistics) have usually been available where the time series dimension t has been small whilst the cross-section dimension n is large. However, nowadays in many applied areas such as marketing, large datasets can be easily collected with n and t both being large. Extracting features from megapanels of panel data is
the subject of bfunctional data analysisQ; see, e.g., Ramsay and Silverman (1997). Yet, the problem of making multi-step-ahead forecasts based on functional data is still open for both theoretical and applied research. Because of the increasing prevalence of this kind of data, we expect this to be a fruitful future research area