Why TREC set two task: document ranking and passage ranking

Question

TREC is https://microsoft.github.io/TREC-2019-Deep-Learning/

I am new to text retrieval. Still can not understand why set the two similar task.

Thank you very much.

Answer 1

The idea behind the two tasks is to explore how document length affects the effectiveness of the different retrieval models.

Ellen Voorhees TREC project manager NIST