Sample /Leaving the other without

Can you please explain what does sample means here?

Either I understood what leaving the other without means here. Thanks for helping

(Video, At 11:24) Today one of the most rigorous scientific methods in the social sciences, where we gave information about self-control to part of the sample, leaving the other part of the sample without such information. The information we gave the people was very similar to the information I just gave you here today about the choices between apples and chocolate.