- A STATISTICAL TEST WHERE THE NULL HYPOTHESIS IS REJECTED IF THE TEST VALUE FALLS INTO EITHER OF THE TWO CRITICAL REGIONS, ONE ON EACH SIDE (TAIL) OF THE MEAN. IT IS USED WHEN THE ALTERNATIVE HYPOTHESIS STATES THAT THERE IS A DIFFERENCE, BUT NOT THE DIRECTION OF THE DIFFERENCE (I.E., THE VALUE COULD BE EITHER SIGNIFICANTLY HIGHER OR SIGNIFICANTLY LOWER THAN THE HYPOTHESIZED PARAMETER)
