Dr. Smith wants to know how best to treat adolescents with depression. Dr. Smith wants to know if length of daily exposure to a sun lamp helps in treating self-reported depression using the BECK's depression index. Dr. Smith asks all of her clients at her clinic to participate in the study. She then randomly assigns 100 participants to receive either 0, 15 minutes or 60 minutes in a tanning booth. 1. What is the IV? 2. How many levels are in the IV and what are they specifically? 3. What is the DV? 4. How was the sample obtained? 5. Did the experimenter exert control in their design? Explain why or why not. 6. Does this study have external and internal validity? (Explain) 7. What is one possible confound in this study? 8. What is a possible threat to validity in this study? (Explain it