📊 4 Diagnostic Plots
// pilih scenario, lihat 4 plot diagnostik klasik (R-style)
1. RESIDUAL VS FITTED (linearity, homosk)
3. SCALE-LOCATION (homosk sensitive)
4. RESIDUAL VS LEVERAGE (influence)
Healthy regresi: Plot 1 random scatter sekitar 0. Plot 2 titik di garis 45°.
Plot 3 horizontal trend. Plot 4 tidak ada titik di luar Cook's contour.
Coba scenario lain: Heteroskedastisitas → plot 1 funnel + plot 3 upward.
Non-linearity → plot 1 curve pattern. Outlier → plot 4 ada titik jauh.