Problem: Julian placed a large plain box labeled 'clothing donations to help local kids' at the grocery store. After leaving the box in place for one week, he removed the contents and counted articles of clothing. The following week, Julian added several photos of small children to the box. After the photos had been attached to the box for one week, Julian again removed the contents and counted the articles of clothing. Julian's research method is best categorized as:
1. Survey
2. A field study
3. Interview
4. A field experiment