- Example: Age of Pitchers (Summarized Data)

Example: Estimating the average MLB Pitcher's age Section

In a sample of 30 current MLB pitchers, the mean age was 28 years with a standard deviation of 4.4 years. Construct a 95% confidence interval to estimate the mean age of all current MLB pitchers.

We know that n = 30, \(\bar{x}=28\), and s = 4.4.

To create a 95% confidence interval of mean age in Minitab:

  1. In Minitab, select Stat > Basic Statistics > 1-sample t
  2. In this case we have summarized data so select Summarized Data from the dropdown
  3. Enter 30 for the sample size, 28 for the sample mean and 4.4 for the standard deviation.
  4. Select Options
  5. The default Confidence level is 95
  6. Click OK and OK

This should result in the following output:

Descriptive Statistics




SE Mean

95% CI for \(\mu\)





(26.357, 29.643)

\(\mu\): population mean of sample

We are 95% confident that the population mean age is between 26.357 and 29.643 years.