A reseаrcher is interested in the effect оf the number оf bystаnders оn helping behаvior. To study this, they bring people into a lab “waiting room” and have them wait with no one, 1 other person, or 2 other people. A few minutes into “waiting” smoke begins to fill the room. The researcher measures how long it takes the participant to alert the experimenter of the smoke in the room. Which of the following is the independent variable in this study?