Statistics and Probability Letters vol. 33, no. 2, pp. 177 - 184
Based on symmetric estimation and the weighted symmetric estimation of Pantula et al. (1994) and Park and Fuller (1995), new semiparametric tests for testing a unit root under the general situation of Phillips (1987) and Phillips and Perron (1988) are developed. A Monte-Carlo simulation shows that the new tests have better power than the semiparametric tests of Phillips (1987) and Phillips and Perron (1988), under first-order moving average errors.