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[摘要]：This paper investigates the trend in the monthly real price of oil between 1990 and 2008 with a generalized autoregressive conditional heteroskedasticity (GARCH) model. Trend and volatility are estimated jointly with the maximum likelihood estimation. There is long persistence in the variance of oil price shocks, and a GARCH unit root (GUR) test can potentially yield a significant power gain relative to the augmented Dickey-Fuller (ADF) test. After allowing for nonlinearity, the evidence supports a deterministic trend in the price of oil. The deterministic trend implies that influence of a price shock is transitory and policy efforts to restore a predictable price after a shock would be unwarranted in the long run. |
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