A threshold AR(1) model

Abstract
We consider the modelwhereφ1,φ2are real coefficients, not necessarily equal, and theat,'s are a sequence of i.i.d. random variables with mean 0. Necessary and sufficient conditions on theφ's are given for stationarity of the process. Least squares estimators of theφ's are derived and, under mild regularity conditions, are shown to be consistent and asymptotically normal. An hypothesis test is given to differentiate between an AR(1) (the caseφ1=φ2) and this threshold model. The asymptotic behavior of the test statistic is derived. Small-sample behavior of the estimators and the hypothesis test are studied via simulated data.

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