Finding t critical values for Confidence Interval – sigma unknown


First, find the t-critical value for right-tailed tests. There are two steps to find it.

  • However, before starting check to see if the population standard
    deviation,σ, is given or not.
    Check the second condition, either the sample size is more than or
    equal to 30 or the population is normally distributed.

    • Step 1, identify the significance level, α as 1 tailed area.
    • Step 2, find the degrees of freedom by subtracting 1 from the sample size. Then look up the table.
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