How to Decide if a Hypothesis Test is a One Tailed Test or a Two Tailed Test

Hypothesis testing 4 Comments

In a hypothesis test, you are asked to decide if a claim is true or not. For example, if someone says “all Floridian’s have a 50% increased chance of melanoma”, it’s up to you to decide if this claim holds merit. But the first step is to look up a z-value, and in order to do that, you need to know if it’s a one-tailed test or a two-tailed test. Luckily, you can figure this out in just a couple of steps.

Sample question #1: A government official claims that the dropout rate for local schools is 25%. Last year, 190 out of 603 students dropped out. Is there enough evidence to reject the government official’s claim?
Sample question #2: A government official claims that the dropout rate for local schools is less than 25%. Last year, 190 out of 603 students dropped out. Is there enough evidence to reject the government official’s claim?
Sample question #3: A government official claims that the dropout rate for local schools is greater than 25%. Last year, 190 out of 603 students dropped out. Is there enough evidence to reject the government official’s claim?

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?)

Related posts:

  1. How to Decide if a Hypothesis Test is a Left-Tailed Test or a Right-Tailed Test.
  2. How to Find a Critical Value for a Right-Tailed Test
  3. How to Find a Critical Value for a Left-Tailed Test
  4. How to find a critical value in statistics (two-tailed test)
  5. How to Support or Reject a Null Hypothesis (for a Proportion)
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4 Responses to “How to Decide if a Hypothesis Test is a One Tailed Test or a Two Tailed Test”

  1. How to Do Everything Statistics » How to Decide if a Hypothesis Test is a Left-Tailed Test or a Right-Tailed Test. said:

    Nov 04, 09 at 11:20 am

    [...] 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 [...]

  2. Rebecca Gamble said:

    Nov 07, 09 at 11:06 pm

    The wording of the problems helps me understand if there is a left, right or two tail tests. for example if the problem does not give a less then or greater then amount, but exact amount then I know that the test it two tailed.

  3. Donna Allen said:

    Nov 13, 09 at 1:44 am

    Thank you for posting this. Your explanation was very helpful. This clearly shows how to tell the difference.

  4. Vanessa DuBarry said:

    Nov 20, 09 at 4:42 pm

    This post makes it more clear now, I didnt know how to tell what kind of test they are but after seeing this its so much easier. thanks professor!

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