An elementary school principal wants to know the mean number of children in families whose children attend this school. He checks all the families using the school's registration records, and we use the computer to create a 95% confidence interval based on a t-distribution. This procedure was not appropriate. Why?
A) The recent record-setting family with twelve children is probably an outlier.
B) The entire population of families was gathered so there is no reason to do inference.
C) At a given school families are not randomly selected.
D) Since these families are from only one school, the family sizes may be skewed.
E) The population standard deviation is known, so he should have used a z-model.

Question

Quizplus · Accepted Answer

Since the principal checked all families in the school's registration records, there is no need for inferential statistics. The sample size is equal to the population size, and there is no sampling error involved. Therefore, a confidence interval based on a t-distribution is not appropriate.

An Elementary School Principal Wants to Know the Mean Number