This means that the conductors of the experiment had direct control over this factor of the experiment and could vary it in order to see how it affected outcomes. In this case, that variable was how intimate the contact was between the experimental subject of the experiment and the “authority figure”, the person instructing the subject to administer pain. The experimenters wanted to see if having the authority figure right there beside the subject giving instructions, as opposed to phoning in instructions, was a factor in the subject’s behavior.