Some research in environmental psychology suggests that incorporating biophilic elements into the workspace can help mitigate the impact of environmental stressors. To investigate this, a researcher conducts a field experiment to examine the effect of installing an active green living wall in the open-plan office of 'Zenith Holdings' (a city-centre financial firm with 220 employees aged 22 to 60) on the self-reported stress levels of the employees.
Identify the independent variable in this study.
