# Example of 1-Sample t

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.

1. Open the sample data, FamilyEnergyCost.MTW.
2. Choose Stat > Basic Statistics > 1-Sample t.
3. From the drop-down list, select One or more samples, each in a column and enter Energy Cost.
4. Select Perform hypothesis test.
5. In Hypothesized mean, enter 200.
6. Click OK.

## Interpret the results

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.