Final answer:
Observational research can vary in duration from a few hours to several weeks or longer, and involves observing subjects' natural behavior without intervention from the researcher.
Step-by-step explanation:
The research that can last for a short duration, such as two hours observing teenagers shop for clothing in a mall, or for longer spans like days or weeks staying with families to observe their use of products, is known as Observational research. This type of research typically involves monitoring the behavior of subjects without any intervention from the researcher. An observational study might seek to gather in-depth insights into natural behaviors as they unfold in real-life settings, whether they are short-term or extend over a longer period. Notable examples include the Strange Situation by Mary Ainsworth to evaluate infant and caregiver attachment styles, and research on issues where experimental studies would be unethical or impractical, such as the effects of smoking on health.