An economist wants to determine whether the monthly energy cost for families has changed from the previous year, when the mean cost per month was $200. The economist randomly samples 25 families and records their energy costs for the current year.

The economist performs a 1-sample t-test to determine whether the monthly energy cost differs from $200.

- Open the sample data, FamilyEnergyCost.MTW.
- Choose .
- From the drop-down list, select One or more samples, each in a column and enter Energy Cost.
- Select Perform hypothesis test.
- In Hypothesized mean, enter
`200`. - Click OK.

The null hypothesis states that the mean of the energy costs is $200. Because the p-value is 0.000, which is less than the significance level of 0.05, the economist rejects the null hypothesis and concludes that the average monthly energy cost for families differs from $200. The 95% CI indicates that the population mean is likely to be greater than $200.

N | Mean | StDev | SE Mean | 95% CI for μ |
---|---|---|---|---|

25 | 330.6 | 154.2 | 30.8 | (266.9, 394.2) |

Null hypothesis | H₀: μ = 200 |
---|---|

Alternative hypothesis | H₁: μ ≠ 200 |

T-Value | P-Value |
---|---|

4.23 | 0.000 |