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.
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.