Which of the following describes a research scenario that qualifies as involving human subjects?

The scenario involving an observational study of toddlers' interactions qualifies as involving human subjects because it directly observes and gathers information from living individuals, specifically the toddlers in this case. In research ethics, a human subject is typically defined as a living individual about whom an investigator (whether professional or student) conducting research obtains data through intervention or interaction with the individual or obtains identifiable private information.

Observing toddlers' interactions falls within this definition since the study actively engages with the behaviors and interactions of living subjects, allowing researchers to gather personal and identifiable data related to a specific demographic. This direct interaction underpins the need for ethical considerations, informed consent, and protocols outlined in research involving human subjects to ensure their rights and welfare are protected.

The other scenarios do not qualify as involving human subjects in the same way. Sending a survey via email can involve human subjects, but it depends on how the data is collected and whether there's direct interaction or identifiable information involved. A literature review only involves analyzing existing published studies and does not require engagement with living individuals. Lastly, studying archived medical records might include data from human subjects, but since these are historical records often stripped of personal identifiers, it doesn’t involve direct interaction or engagement with individuals currently.