Outlier detection and time series modeling
Technometrics
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This paper reports the results of a study of outlier detection in time series data for the outlier of level change (LC) type. The main objective is to derive a test statistic for detecting LC in GARCH (1,1) processes. Subsequently a procedure for testing the presence of outliers using the statistics was developed. In the derivation of the statistics, the method applied was based on an analogy of GARCH (1,1) as being equivalent to ARMA(1,1) for the residuals εt2. Because of the difficulty in determining the sampling distributions of the outlier detection statistics, critical regions were estimated through simulations. The developed outlier detection procedure was applied for testing the presence of LC outliers in the daily observations of the Index of Consumer Product Price (ICP) for the period 1990 to 2005. Over the period, the results indicate that LC outlier occurred in year 1998.