Question

How would results vary between observing a population directly as opposed to observing them indirectly?

Answer 1

The results would vary between observing a population directly as opposed to observing them indirectly in a way that you will miss some factors, particularly, those observable factors, such as their daily and actual behavior. Hope this answers your question.

Answer 2

Direct observations are made on subjects by recording the behaviours they exhibit in their natural setting. The researcher can either be physically present to record these observations using a camera or can hide to avoid any interference in the data gathering process. Example, watching or recording a bird chirp.

Indirect observation involves recording the traces left by the subject to understand the reason behind the behaviours exhibited by a subject. Example,    observing the distribution of bird droppings to figure out their movement.

Thus, a direct observation will help identify the behaviours in a population and an indirect observation will establish the reason behind the observed behaviours in the population.