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When calculating the P-value, must you change the sign of the test statistic?

  1. Nov 26, 2012 #1
    1. The problem statement, all variables and given/known data
    When calculating the P-value, must you change the sign of the test statistic depending on the type of test (lower, upper)?

    For example, if your calculated test statistic is t=2.5 and you want to perform a lower-tailed test, is your answer the cumulative probability of 2.5 or -2.5?

    I ask because there are no similar examples in my textbook. All the problems for lower-tailed tests use negative test statistic values, and all the problems for upper-tailed tests use positive test statistic values.

    There is one odd-numbered problem asking for an upper tailed test with z= -2.2, and the answer is given as the complement of the cumulative probability of -2.2. since this is the only problem like this given, I don't know if it is right or not.

    Because if so, then I get answers such as 0.9983 for the P-value.

    Thanks.
     
  2. jcsd
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