Confidence Intervals for μ (when σ is unknown and n<30)

Suppose that you are creating a 95% confidence interval for the average pH of a lake; however, you do not know the population standard deviation.

The data is 7.8, 7.5, 7.4, 7.8, 6.9, 6.8, 6.5, 6.7, 6.9, and 6.3

When sigma is unknown and n<30, you want to conduct a confidence interval that uses t.

1. To do this, enter your data into C1. Then go to Stat, Basic Statistics, 1 sample t.
2. Your screen should look like this.

3. Now, input the data.
1. If you have the data listed in a column in the worksheet, simply type in the column number in the Samples in columns box.
2. If you do not have the data, list the mean, sample size and standard deviation in the box provided under Summarized Data.

4. Make sure that you entered the correct confidence level.
5. Next pick the type of confidence interval or bound.
1. If you want a confidence interval select, "not equal" as your alternative.
2. If you want a confidence bound, select "less than" for a upper bound or "greater than" for an lower bound.
6. Your output should look similar to the output below.

One-Sample T: C1

Variable N Mean StDev SE Mean 95% CI

C1 10 7.06000 0.53166 0.16813 (6.67967, 7.44033