Question

Seligman's study in which he created learned helplessness in the lab is an example of a(n) ______ study.

Answer 1

I believe the answer you are looking for is "case study" 
A case study is a publication of an experience conducted over an amount of time. It could be based on behavior for each or a group. 

Answer 2

Seligman's study in which he created learned helplessness in the lab is an example of a(n) Answer—> case study.

Case study’s are in-depth investigations of a single person, group, event or community