"I am not sure how many sessions I should check whether each of them has single or multiple information need."

"So, how many sessions you've checked?"

"about 2000."

"Wao... that's enough, much more than necessary."

"囧rz..."

"Another question is, how many sessions I should used for experiment? I am not sure how many is enough."

"How many do you have now?"

"About 50000. Including the data needed for checking information need."

"Oh, that quite a lot. Actually, I think 50 or 100 are enough." 

"囧rz... 囧rz... 囧rz... 囧rz..."