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

Hypothesis testing 8 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.

Area under a normal distribution curve (one tail)

Area under a normal distribution curve (one tail)

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.

Related posts:

  1. How to Decide if a Hypothesis Test is a One Tailed Test or a Two Tailed Test
  2. How to Find a Critical Value for a Left-Tailed Test
  3. How to Find a Critical Value on a Ti-89 Titanium (Left-Tailed test)
  4. How to Find a Critical Value for a Right-Tailed Test
  5. How to find a critical value in statistics (two-tailed test)
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8 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?) [...]

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