In the context of improving defect rates with a confidence interval, is the hypothesis test one-tailed or two-tailed?

In the context of improving defect rates with a confidence interval, a one-tailed hypothesis test is appropriate because the focus is typically on examining whether the defect rate has specifically decreased (improved) compared to a prior measurement.

A one-tailed test allows you to test for a change in one direction—specifically, checking if the defect rate is lower than a certain threshold. This approach is relevant when you are only interested in determining whether there is a significant reduction in defect rates, rather than considering both increases and decreases.

On the other hand, a two-tailed test would be used if the hypothesis were concerned with any change in defect rates, either an increase or a decrease, which is not the focus when the intention is specifically to assess for improvement. Therefore, the correct answer reflects the directionality of the hypothesis test when evaluating the improvement of defect rates.