# 9.2.1.1 - Minitab Express: Confidence Interval Between 2 Independent Means

9.2.1.1 - Minitab Express: Confidence Interval Between 2 Independent MeansMinitab Express can be used to construct a confidence interval for the difference between two independent means. Note that the confidence intervals given in the Minitab Express output assume that either the populations are normally distributed or that both sample sizes are at least 30.

## MinitabExpress – Confidence Interval Between 2 Independent Means

Let's estimate the difference between the mean weight (in pounds) of females and the mean weight of males. Both sample sizes are at least 30 so the sampling distribution can be approximated using the *t* distribution.

- Open the Minitab Express file:
- On a
**PC**: In the menu bar select**STATISTICS > Two Samples > t**

On a**Mac**:**Statistics > 2-Sample Inference > t** - Double click the variable
*Weight*in the box on the left to insert the variable into the*Samples*box - Double click the variable
*Gender**Sample IDs*box - Click OK

This should result in the following output:

\(\mu_1\): mean of Weight when Gender = Female |

\(\mu_2\): mean of Weight when Gender = Male |

Difference: \(\mu_1-\mu_2\) |

*Equal variances are not assumed for this analysis.*

Gender | N | Mean | StDev | SE Mean |
---|---|---|---|---|

Female | 126 | 136.722 | 23.362 | 2.081 |

Male | 99 | 172.717 | 27.301 | 2.744 |

Difference | 95% CI for Difference |
---|---|

-35.995 | (-42.787, -29.202) |

Select your operating system below to see a step-by-step guide for this example.

I am 95% confident that in the population the mean weight of females is between 29.202 pounds and 42.787 pounds less than the mean weight of males.