1 and 2 tailed hypothesis testing

[sbmfj]

Hi,
Regarding 1 and 2 tailed tests, how do you tell if the question is asking you for a 1 tailed or 2 tailed test?
The ‘null’ is what we are trying to reject, right?
Ive always had a hard time with those.
thanks

 

[florinpop]

2 tailed test - try to prove that null is significantly different(considering confidence intervals) than a value- (that is rejecting the null) and that might happen if your value is outside the confidence intervals either on the left or right of the distribution-use = for null
1 tailed test - try to prove for ex that the null is to the left (or to the right of the confidence intervals)-depending on the example-use = for the null

 

[lillilland]

To help distinguish between 1 or 2 tailed, you can tell by the question they are asking:
For a 1-tailed test, look for words like “better than”, “worst than”, something that implies a one-sided comparison. For example, Did A perform BETTER than B.
For a 2-tailed test, look for words like “any difference”, something that conveys that they dont care if what you’re testing is better or worse than status quo, as long as its different. For example, Did the expected return change from X?
Hope that helps.