Figure 2.

The meta-population ℜ₀ as a function of fractions of the contacts that members of two sub-populations reserve for others within their own sub-populations (ε₁, ε₂) when their activities (average contact rates) are more or less heterogeneous. ℜ₀ decreases from the top surface (a₁ = 4, a₂ = 16), through the middle (a₁ = 8, a₂ = 12), to the bottom (a₁ = a₂ = 10). See table 1 for other parameter values. As heterogeneity in ε(e.g., ratio of the variance and mean) increases away from the line ε₁ = ε₂, heterogeneous preferential mixing also increases ℜ₀.