What does T equal?? pls help

Pls me this is due today and i need i will make brainliest if you me answer correctly and i will report if you try to give me a dumb answer.

An energy drink company claims that its product increases students' memory levels. to support its claims, the company issues advertisements claiming that 8 out of 10 people (chosen randomly from across the country) who tried their product reported improved memory. the missing component in this study is a .

Ihonestly have no clue if it's each or none.