Social learning rules and the effectiveness of behavioural policy: an agent-based model

Behaviour-change interventions unfold in social systems where people learn from others. We develop a stylised agent-based model to examine how four canonical social learning rules – conformist transmission, informational prestige-biased copying, payoff-biased copying and random copying – shape the impact of a simple seeding intervention. Two arms evolve under identical conditions and learning rules, differing only in initial adoption: both start with exactly 5% baseline adopters and the treatment arm additionally seeds 20% of the remaining non-adopters, yielding an exact 25% vs 5% contrast at 𝑡 =0. Across homogeneous populations, 70/30 mixed ecologies and sweeps over the share of payoff-biased learners, we track adoption trajectories and treatment–control lift; we also vary payoff parameters, prestige informativeness and conformist thresholds in robustness analyses. We find that the same seeding intervention can stall, drift or cascade depending on the learning ecology. In the baseline specification, conformist dynamics exhibit threshold effects that erase treatment gains, prestige-biased and random copying can preserve positive final lift when diffusion remains incomplete and payoff-biased copying mainly changes the diffusion regime rather than preserving large end-point gaps. Robustness checks show that negative payoff premia suppress diffusion, weak or noisy payoff signals can generate treatment advantages, prestige effects depend on how informative prestige is and conformist treatment effects are concentrated in narrow threshold-boundary regions. These results motivate policy heuristics that evaluate interventions relative to local diffusion potential, make successful outcomes visible when payoff cues matter and tailor seeding to the prevailing mix of learning rules.