## How to Decide if a Hypothesis Test is a Left-Tailed Test or a Right-Tailed Test.

In a hypothesis test, you have to decide if a claim is true or not. The first step is to decide if you have a one-tailed test or a two-tailed test (How to decide if a hypothesis test is a one-tailed test or a two-tailed test) , then you need to decide if it’s a left-tailed test or a right-tailed test in order to figure out the z-score. This takes one step!

Sample hypothesis #1: drop out rate Sample hypothesis #2: drop out rate >75%
Step 1: Draw a normal distribution curve. Assume the area under the curve equals 100%, then shade in the related area.
This picture represent the phrase “less than 25%”. You can see that it would be a left-tailed test.

The yellow area could illustrate the area greater than 75%. From this diagram you can clearly see that it is a right-tailed test (because the shaded area is on the right.

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## 9 Responses to “How to Decide if a Hypothesis Test is a Left-Tailed Test or a Right-Tailed Test.”

1. ### Donna Allen said:

Nov 13, 09 at 1:52 am

Thank you for posting this. It seems simpler, now. Once I saw the graph it helped me visualize what the word problem is saying.

2. ### Jennifer Thomas said:

Nov 17, 09 at 6:14 pm

Thank you. I went through this chapter not understanding how to determine this. I didn’t realize how easy it really was. Now if I can only grasp when to reject and when to accept a claim! :0)

3. ### Vanessa DuBarry said:

Nov 20, 09 at 4:36 pm

Yes by looking at this example it makes more sense and it does make it a little bit easier. And by this I learned the importance of drawing this graphs to get the answer.

4. ### Rebecca Gamble said:

Dec 17, 09 at 11:30 am

Even after completing the final I still do not understand hypotheses. Its like greek! And i hate not understanding this, because according to some this was the easiest section in Statistics.

5. ### apbryant89 said:

Mar 29, 10 at 7:15 pm

I think I finally get it, for some reason the physical representations help alot.

6. ### Stanley said:

Aug 01, 10 at 11:39 am

Thank god. This just helped me understand whether its left or right tailed.

7. ### Mike said:

Aug 25, 11 at 2:21 am

Thanks this really helped me understand something very important which my college lecturers notes didn’t explain

8. ### Statistics How To» Blog Archive » How to Decide if a Hypothesis Test is a One Tailed Test or a Two Tailed Test said:

Jan 03, 12 at 11:36 am

[...] Step 1: Read the question. Step 2: Rephrase the claim in the question with an equation. In sample question #1, Drop out rate=25% In sample question #2, Drop out rate In sample question #3, Drop out rate>25%. Step 3: If step 2 has an equal sign in it, this is a two-tailed test. If it has > or (How do I tell if a hypothesis test is left-tailed or right-tailed?) [...]

9. ### soufi said:

Jun 15, 12 at 11:41 am

thanks so much