A teacher is trying to see whether smiling at her students will increase the number of questions they ask. In the first and third week of the study, the number of questions students ask is recorded. In the second week, the teacher smiles a lot at her students, and the number of questions is also recorded. What type of research design is being used?
◦ within-subjects
◦ correlational
◦ placebo control
◦ between-subjects