Final answer:
Peter Stearns gathered secondary data from existing sources for his book, avoiding the alteration or influence of subject behavior, characteristic of nonreactive research.
Step-by-step explanation:
Peter Stearns consulted various existing sources for his book Anxious Parents: A History of Modern Childrearing in America. What he found was secondary data from existing sources rather than primary data through surveys, experimental data from controlled studies, or qualitative data through interviews. This means that the information Stearns used was based on the already completed work of other researchers or data collected by an agency or organization, such as books, articles, periodicals, newspapers, or magazines. The nature of secondary data is that it is nonreactive research, meaning it does not involve direct contact with subjects and hence does not alter or influence people's behavior, which makes it an unobtrusive form of research.