Look out for treatment comparisons where people knew which treatment they received and knowing that could have changed how they felt or behaved.
In cases where people may benefit from exposure to certain environments, people who are exposed may feel better (for example, they may have less stress) because they believe they are getting a beneficial exposure and expect that will make them feel better. This can happen even if the treatment isn’t actually better than the comparison. It is called a “placebo effect”.
Knowing which treatment they got and having expectations about it can also change the way people behave. For example, someone who is told that exercising in a green space will help them reduce stress may also start exercising more. So they may benefit because of those changes, rather than because of the treatment.
REMEMBER: Think about whether the people in the comparison groups knew which treatment they received and, if so, whether that may have changed how they felt or behaved.