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

Hypothesis Testing 9 Comments

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.

right of z score2

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.

Feel like Cheating at Statistics? This is the Statistics Handbook that your professor doesn't want you to see. So easy, it's Practically Cheating. Find out more »
Need more help? Ask on our free forums »

You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.

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