Grayson, a graduate student, wants to better understand the lives of the unhoused population in his city. Over a period of 6 months he immersed himself with this community, conducting interviews, taking photographs, and making observations. Based on this information, what type of research is Grayson conducting?

A research team is investigating the effects of social media use on adolescent mental health. They hypothesize that teens who spend more than 1 hour a day using social media platforms will have poorer mental health compared to adolescents who spend less than 1 hour. In this research study, what is the independent variable?