Jean piaget based his ideas about infants' cognitive development on his detailed observations of his own three children. this is an example of what research method?

Case Study

Explanation:                    

Case Study -

It is the type of research method , where the in depth investigation about a particular object , person , community or group is done , is referred to as case study.

In this research method , the data and information is collected from various sources available , in order to have a wider range of information .

This research method , is mainly used in the field of psychology .

Hence , from the given example of the question,

The correct term is case study.

answer; self-efficacy;