Question

What is the reasoning behind the use of a two-tailed test in a research project? Why are the absolute values of the critical values in a two-tailed confidence interval the same?

Answer 1

In a research analysis, we are usually concerned with whether a population parameter is different from a certain value. So, the null hypothesis is the claim, of a particular value of the population parameter. And the alternate hypothesis is whether the parameter is different from the particular value.

So, usually, the tests are two tailed.

In a two tailed test, the statistic values are the opposite signs of each other. So, the dritical values are also negative of each other.

So, the absolute values of the critical values, are the same.