Which study qualifies as research involving human subjects according to federal regulations?

The study that qualifies as research involving human subjects according to federal regulations is the videotaping of toddler interactions. This is because federal regulations define "human subjects" as individuals from whom data is collected through intervention or interaction, or whose private information is obtained. In this case, videotaping toddlers involves directly interacting with them and collecting data about their behavior, thus making them human subjects.

The other options, while they may involve human behavior or data, do not meet the criteria of interacting with individuals in a way that directly collects data from them or their private information. For example, the analysis of aggregate data analyzes information without involving direct contact or individual interactions with personal data. Similarly, a survey of consumer preferences may not involve necessary interactions that qualify it as research with human subjects if it does not involve identifiable individuals. An observational study of public behavior is typically conducted in a manner where individuals can remain anonymous, generally not qualifying as research that involves human subjects under federal regulations.