Complex Contagion
Simple contagion (disease) spreads with one exposure. Complex contagion (social behavior, beliefs) requires multiple reinforcing signals — fraction θ of neighbors must be active. This creates hysteresis and discontinuous transitions.
Adopt if: (active neighbors)/k ≥ θ
Simple: θ → 0 (one trigger)
Complex: θ > 0 (social proof needed)
Cascade: giant component if ⟨k²⟩/⟨k⟩ > 1/θ
Simple: θ → 0 (one trigger)
Complex: θ > 0 (social proof needed)
Cascade: giant component if ⟨k²⟩/⟨k⟩ > 1/θ
Spreading Model
Simple
Complex
Hybrid
0%
Adopted
—
Cascade
0
Rounds
0
Seed nodes