An investigator wanted to see whether packaging information affects the way teenagers rate the effectiveness of soap. the same soap was put in three packages: (a) a pink wrapper that says "for keeping your skin baby soft," (b) a red wrapper that says "for eliminating acne," and (c) a white wrapper that says nothing. each teenager was asked to rub his or her face with dirt and wash with soap a; the same procedure was followed for soaps b and then c. the time it took to get the face clean was recorded each time. what factors in addition to the intended independent variable might influence the results?