Advertisers are often interested in knowing things such as the age of the youngest child, the size of the family, and the family income. The age of the youngest child at home tells an advertiser where the family is in terms of its needs and obligations (i.e., toys, investments for college savings, clothing, and vacations). When the youngest child leaves home, the family's consumption patterns change. Advertisers like to track the age of the youngest child living at home and use it as a planning criterion. This is known as the _______________.