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"Frontmatter". In: Analysis of Financial Time Series

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<strong>Analysis</strong> <strong>of</strong> <strong>Financial</strong> <strong>Time</strong> <strong>Series</strong>. Ruey S. TsayCopyright © 2002 John Wiley & Sons, <strong>In</strong>c.ISBN: 0-471-41544-8CHAPTER 2Linear <strong>Time</strong> <strong>Series</strong> <strong>Analysis</strong>and Its Applications<strong>In</strong> this chapter, we discuss basic theories <strong>of</strong> linear time series analysis, introducesome simple econometric models useful for analyzing financial time series, andapply the models to asset returns. Discussions <strong>of</strong> the concepts are brief with emphasison those relevant to financial applications. Understanding the simple time seriesmodels introduced here will go a long way to better appreciate the more sophisticatedfinancial econometric models <strong>of</strong> the later chapters. There are many time seriestextbooks available. For basic concepts <strong>of</strong> linear time series analysis, see Box, Jenkins,and Reinsel (1994, Chapters 2 and 3) and Brockwell and Davis (1996, Chapters1–3).Treating an asset return (e.g., log return r t <strong>of</strong> a stock) as a collection <strong>of</strong> randomvariables over time, we have a time series {r t }. Linear time series analysisprovides a natural framework to study the dynamic structure <strong>of</strong> such a series. Thetheories <strong>of</strong> linear time series discussed include stationarity, dynamic dependence,autocorrelation function, modeling, and forecasting. The econometric models introducedinclude (a) simple autoregressive (AR) models, (b) simple moving-average(MA) models, (c) mixed autoregressive moving-average (ARMA) models, (d) seasonalmodels, (e) regression models with time series errors, and (f) fractionally differencedmodels for long-range dependence. For an asset return r t , simple modelsattempt to capture the linear relationship between r t and information available priorto time t. The information may contain the historical values <strong>of</strong> r t and the random vectorY in Eq. (1.14) that describes the economic environment under which the assetprice is determined. As such, correlation plays an important role in understandingthese models. <strong>In</strong> particular, correlations between the variable <strong>of</strong> interest and its pastvalues become the focus <strong>of</strong> linear time series analysis. These correlations are referredto as serial correlations or autocorrelations. They are the basic tool for studying astationary time series.22

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