I believe the answer is: physical development
In longitudinal study same subjects over a certain period of time. From the study above, we can see that on-field-performance is the dependent variables. Since there is no way for the researchers to conduct and proof the psychological development, physical development ia the most suitable choice.
The type of research method which the researcher is using is known as:
<h3>What is Research?</h3>
This refers to the systematic study of a phenomena so as to understand the why, where and how and how to possibly replicate the situation with the aid of scientific method.
With this in mind, we can see that the said researcher who is observing young children playing without obstructing or intervening is making use of the research method known as naturalistic observation.
Read more about research here:
brainly.com/question/968894
