A researcher wants to know if people report an elevated mood after writing with a colorful pen. A group of 20 students is first asked to write with a basic black pen and report their mood on a scale from 1 to 7 (they can use any number between 1 and 7, even a decimal). A week later, they are given a colorful pen and again asked to report their mood on the same scale. The researcher then compares the ratings for each person.
This is an experiment. WHY? (Your answer should tell me why this is an experiment, specifically, and not another type of study.)