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

[nontradstuden]

Homework Statement

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.

 

[lippyka]

Homework Equations The Attempt at a Solution Yes, you must change the sign of the test statistic depending on the type of test (lower, upper). If you want to perform a lower-tailed test, your answer should be the cumulative probability of -2.5. The problem with an upper tailed test with z = -2.2 is correct and the P-value should be 0.9983.