TY - JOUR TI - Testing for a Unit Root in a Time Series With a Changing Mean AU - Pierre PerrĂ³n JO - Journal of Business and Economic Statistics PY - 1990 VL - 8 IS - 2 DO - 10.1080/07350015.1990.10509786 UR - https://doi.org/10.1080/07350015.1990.10509786 ER -