# 9.2.1.1 - Minitab: Confidence Interval Between 2 Independent Means

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

##
Minitab^{®}
– 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 file: class_survey.mpx
- Select
*Stat > Basic Statistics > 2 Sample t* - Select
*Both samples are in one column*from the dropdown - Double click the variable
*Weight*in the box on the left to insert the variable into the*Samples*box - Double click the variable
*Biological Sex**Sample IDs*box - Click OK

This should result in the following output:

##### Method

\(\mu_1\): mean of Weight when Biological Sex = Female

\(\mu_2\): mean of Weight when Biological Sex = Male

Difference: \(\mu_1-\mu_2\)

*Equal variances are not assumed for this analysis.*

##### Descriptive Statistics: Weight

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

Female | 126 | 136.7 | 23.4 | 2.1 |

Male | 99 | 172.7 | 27.3 | 2.7 |

##### Estimation for Difference

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

-35.99 | (-42.79, -29.20) |

#### Interpret

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.