What is a two-tailed hypothesis?

What is a two-tailed hypothesis?

• A. A hypothesis that predicts a relationship but does not specify the direction.
• B. A hypothesis that predicts a positive direction only.
• C. A hypothesis that the null is two times false.
• D. A hypothesis tested with two-tailed p-values.

Answer: (A)

A two-tailed hypothesis is one that looks for an effect in either direction, not specifying whether the effect will be increase or decrease. The alternative hypothesis states there is some relationship or difference, without predicting its direction. This is useful when you don’t have a strong reason to expect a particular direction. For example, if you’re testing whether a new intervention changes a clinical score, you don’t commit to it improving or worsening the score—only that it will differ from the current condition. Why the other notions don’t fit: predicting a positive direction describes a one-tailed alternative, which narrows the test to one end of the distribution. Saying the null is two times false isn’t a standard definition. The idea of two-tailed p-values relates to the testing procedure, not to what the hypothesis itself states.

A two-tailed hypothesis is one that looks for an effect in either direction, not specifying whether the effect will be increase or decrease. The alternative hypothesis states there is some relationship or difference, without predicting its direction. This is useful when you don’t have a strong reason to expect a particular direction.

For example, if you’re testing whether a new intervention changes a clinical score, you don’t commit to it improving or worsening the score—only that it will differ from the current condition.

Why the other notions don’t fit: predicting a positive direction describes a one-tailed alternative, which narrows the test to one end of the distribution. Saying the null is two times false isn’t a standard definition. The idea of two-tailed p-values relates to the testing procedure, not to what the hypothesis itself states.