Astudy that conducts interviews with mothers of extreme multiple births such a sextuplets is what kind of case study

A study that conducts interviews with mothers of extreme multiple births such a sextuplets is what kind of case study? Case study interviews.

There are many types of case studies, when interviewing people who meet the criteria of being able to give insight to a topic, you are conducing a case study interview. You are interviewing the person or persons' to gain knowledge from their experiences. 

answer; not notated (at least, not in the traditional sense) and includes many improvised sections and solos;