A veterinarian wants to estimate the average weight gain per month of 4-month-old golden retriever pups when placed on a lamb and rice diet. The population consists of the weight gains per month of all 4-month-old golden retriever pups that could be given this particular diet. The veterinarian wants to estimate the unknown parameter m, the average monthly weight gain for this hypothetical population.

One possible estimator based on sample data is the sample mean, x 5Sx n i / . It could be used in the form of a single number or point estimate—for instance, 1.7 kilograms—or you could use an interval estimate and estimate that the average weight gain will be between 1.2 and 2.2 kilograms.