Question

# Is there a relationship between confidence intervals and two-tailed hypothesis tests? Let c be the level...

Is there a relationship between confidence intervals and two-tailed hypothesis tests? Let c be the level of confidence used to construct a confidence interval from sample data. Let α be the level of significance for a two-tailed hypothesis test. The following statement applies to hypothesis tests of the mean.

For a two-tailed hypothesis test with level of significance α and null hypothesis H0: μ = k, we reject H0 whenever k falls outside the c = 1 –  α confidence interval for μbased on the sample data. When k falls within the c = 1 –  α confidence interval, we do not reject H0.

(A corresponding relationship between confidence intervals and two-tailed hypothesis tests also is valid for other parameters, such as p, μ1μ2, or p1p2, which we will study in later sections.) Whenever the value of k given in the null hypothesis falls outside the c = 1 –  α confidence interval for the parameter, we reject H0. For example, consider a two-tailed hypothesis test with α = 0.05 and

H0: μ = 21
H1: μ ≠ 21

A random sample of size 14 has a sample mean x = 19 from a population with standard deviation σ = 5.

(a) What is the value of c = 1 − α?

0.95

Using the methods of Chapter 7, construct a 1 − α confidence interval for μ from the sample data. (Round your answers to two decimal places.)

Lower Limit: 16.38

Upper Limit: 21.62

What is the value of μ given in the null hypothesis (i.e., what is k)?

k = 21

Is this value in the confidence interval?

Yes

Do we reject or fail to reject H0 based on this information?

Fail to reject, since μ = 21 is contained in this interval.

(b) Using methods of Chapter 8, find the P-value for the hypothesis test. (Round your answer to four decimal places.)

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