Students complete the Major Depression Inventory MDI (X), the Rumination Response Scale RRS (Y), and the UCLA Loneliness Scale UPLAS (Z), then collect all three scores from 9 classmates and run two correlations: Depression vs. Rumination and Depression vs. Loneliness. The lab distinguishes between depression's internal cognitive driver (rumination — repetitive negative thought) and its social consequence (loneliness — felt disconnection), asking which is more strongly correlated with depressive