What is a one-tailed hypothesis?

What is a one-tailed hypothesis?

• A. Only one direction of an effect or relationship is predicted in the alternative hypothesis.
• B. The hypothesis predicts two directions.
• C. The null hypothesis is tested in only one direction.
• D. The test statistic is one-tailed in distribution.

Answer: (A)

In a one-tailed hypothesis, you predict the effect will occur in only one direction. This means the alternative hypothesis states a difference or relationship that goes in a single, specified way (for example, the treatment will increase a score or the drug will reduce symptoms), and you reject the null only if the observed statistic falls into that single tail of the sampling distribution. Because the critical region is placed in one direction, the test has more power to detect an effect in that direction, but it misses effects that occur in the opposite direction. This is why the one-tailed approach is used when you have a clear, directional prediction.

In a one-tailed hypothesis, you predict the effect will occur in only one direction. This means the alternative hypothesis states a difference or relationship that goes in a single, specified way (for example, the treatment will increase a score or the drug will reduce symptoms), and you reject the null only if the observed statistic falls into that single tail of the sampling distribution. Because the critical region is placed in one direction, the test has more power to detect an effect in that direction, but it misses effects that occur in the opposite direction. This is why the one-tailed approach is used when you have a clear, directional prediction.