A classic finding in social psychology, the halo effect, is the idea that our overall impression of a person can be based on one trait about them. for example, if someone has a likeable personality, people might find that person's other qualities more appealing. in a recent experiment, a man made two videos for a dating website. in the first video, he read the script in an upbeat manner, whereas in the second, he read the same script in a more melancholy fashion. the first video was given to one group of girls and the second was given to another group, who watched the video in a separate room. the girls who watched the upbeat video found the man to be likeable, while the girls who watched the second video found the man to be unpleasant, even though he had read the exact same script. this may demonstrate the importance of tone in the perception of overall attractiveness. please identify what type of research design this scenario is an example of.

The experiment with two or more parallel groups is one of the first experiments in psychology. This kind of experiment is highly controlled by researches and requires equal groups from which one is the control group and the other is experimental. To both of the groups is shown the same material, in this case a video, but with the slight change (different intonation). If groups show different results, that would be described as the effect of the change (intonation).