In this paper we evaluate the performance of three methods for testing the existence of a unit root in a time series, when the models under consideration in the null hypothesis do not display autocorrelation in the error term. In such cases, simple versions of the Dickey-Fuller test should be...

Showing a dual relationship between ARIMA (0, 2, 1) with parameter θ = -1 and the random walk, a new alternative hypothesis in the form of ARIMA (0, 2, 1) is established in this article for evaluating unit root tests. The power of four methods of testing for a unit root is investigated under...

Given the random walk model, we show, for the traditional unrestricted regression used in testing stationarity, that no matter what the initial value of the random walk is or its drift or its error standard deviation, the sampling distributions of certain statistics remain unchanged. Using Monte...

In this paper, the optimal pollution level is identified under the assumptions of linear, quadratic and exponential cost functions. The corresponding optimal level of environmental policy is evaluated, with analytical forms in the linear and quadratic case, while in the exponential case, these...