The mere-measurement effect means that just by measuring something, people tend to do better at it. It's like when you have a math test coming up and your teacher tells you that they're going to test you on your multiplication tables. You may not have been practicing them before, but now that you know you're going to be tested on them, you start studying and practicing more.
Scientists have found that the mere act of measuring something can have a similar effect on people. For example, if a person knows that they're being observed while performing a task, they may try harder to perform well or avoid mistakes. This is called the Hawthorne effect.
Additionally, when people are asked to rate or evaluate their own behavior, they tend to improve their performance. This is because the act of measuring or evaluating can raise their awareness of their behavior and motivate them to do better.
So, to summarize, the mere-measurement effect means that people tend to improve their performance on tasks or behavior that are measured or evaluated. This happens because the act of measuring or evaluating raises their awareness and motivates them to do better.