Problem: Is this a exampling, design or validity?
Researchers wanted to test the hypothesis that exposure to full color photos of facial expressions would evoke more intense emotional reactions to those same photos shown in monotone. By coin toss, they elected to show each participant the full color photos first and the monotone photos second. Heart rate increase was used to operationalize the intensity of emotional reaction to each photo (note: this is not the problem). Researchers found greater heart rate increases to full color photos and concluded that color caused more emotionally intensive reactions.