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EDITORIAL

This theme issue consists of several papers presented at the NBER/NSF Time Series Conference on September 19 and 20, 2003 in honor of Prof. George Tiao's retirement. In addition, several papers in the same theme topics are selected from our regular submissions. These topics mark the important contributions of Professor Tiao in the areas of Bayesian inference, environmental statistics and time series analysis. We take this opportunity to express our gratitude to him, the founding editor of Statistica Sinica, without whom the journal would not exist.