Every ten years the U.S. Census Bureau mails forms to every home in the U.S. to collect federally mandated data. The Census Bureau is using which data collection method?

Natural observation refers to collecting data by observing subjects in their natural environment without interference or manipulation. This method is not applicable to the Census Bureau's approach, as the Bureau actively solicits information through mailed forms rather than passively observing behaviors or characteristics.

Participant research involves the researcher actively engaging with subjects or participating in the environment being studied. The Census Bureau does not engage in participation; instead, it relies on structured surveys sent to households to gather objective data, which distinguishes it from participant research.

Survey research is characterized by systematically collecting data from a population through questionnaires or interviews. The U.S. Census Bureau exemplifies this method by mailing forms to every household to gather comprehensive demographic information, making this the correct answer.