You are doing an observational study on how students pay attention in the classroom. You want to use a camera to observe them. But since you can not privately record them due to ethical issue, you have to let them know you are making the observation through a camera. The possible outcome of that is students will not act natural since they know you are watching them. Your research will get affected since you can not make a genuine result of the students conduct. This problems is known as

Howthorne effect

Camera shy effect

Replication

Experiment