Dr. Jourdan is interested in how people in small groups interact. She is studying Brittany and her closest friend who meet every Friday for lunch, attend the same church, and are on the same bowling team. This type of study is an example of

micro-level analysis

Explanation:  A micro-level analysis can be simply defined as a type of study in social sciences where analysis are made on the smallest unit possible and their social setting. By smallest unit, it means an individual in their social setting/environment a a very small group of people. So carrying out simple analysis or study on this individual or small group is referred to as micro-level analysis.

Dr. Jourdan is involved  in micro-level analysis/study as his interest is on small group of people and their interaction.