Final answer:
Psychographic segmentation is a marketing tool that gathers information about consumer values, attitudes, interests, and lifestyles. It cannot be used to determine the number of children in a household.
Step-by-step explanation:
Psychographic segmentation is a marketing tool used to gather information about consumer values, attitudes, interests, and lifestyles. It helps marketers understand the psychological and behavioral characteristics of their target market. Based on the options provided, the type of information that cannot be gathered using psychographic variables is option a: knowing how many children under the age of 18 live in the households of the target market. Psychographic variables focus on personal characteristics and preferences, rather than demographics such as the number of children in a household.