Why Isn't the Average Child from the Average Family?: And Similar Puzzles
James J. Jenkins, J. Terrell Tuten · The American Journal of Psychology · 1992
If the average number of children per family in a community is three, it does not follow that the average child has two siblings. Except in a unique circumstance, the number of children in the family of the average child will be greater than the average number of children per family. This seeming contradiction applies to many sets of data. We give a formula for calculating the mean number of children in the family of the average child from the mean and variance of the family distribution. We also discuss the importance of distinguishing the two means in several situations, the critical role played by the variance of the family distribution, and the bias that results if families are sampled via children