Stages of Change: Health Behavior Simulator (2D)

Mode

Time Spent per Stage

Model Parameters

Self-efficacy growth rate γ 0.35

Intervention strength I (support / MI) 0.40

Relapse risk ρ 0.18

Simulated weeks / second 2.0

Cohort size N 200

Live Readouts

Simulated week

Avg. self-efficacy

—

In Action+Maintenance

—

Cumulative relapses

How it works

Every simulated individual carries a self-efficacy value SE ∈ [0,1] (Bandura) and sits in one of Prochaska & DiClemente's five stages of change. Each simulated week the same discrete-time Markov-chain step runs, exactly as in the 3D version of this simulator:

SE(t+1) = SE(t) + γ · (1 − SE(t)) · (0.15 + I)

Decisional balance:  DB = clamp(0.6·I + 0.4·SE − 0.25, 0, 1)
Forward-stage rate:  λ_fwd = 0.22 · SE · DB
Relapse rate (Action/Maintenance only):
                     λ_relapse = ρ · (1 − SE)

P(transition this week) = 1 − e^(−λ)

Individual mode — one person is advanced week by week; the state-machine diagram above highlights their current stage and the edge labels show the exact probability of moving along each arrow *this* week, computed live from their own SE.
Population (Monte Carlo) mode — N independent people are simulated in parallel with the identical per-agent rule; the chart becomes a stacked area plot of what fraction of the cohort occupies each stage as weeks pass, which is the real emergent distribution implied by the transition probabilities, not a scripted curve.
Self-efficacy growth γ — how fast confidence in one's own ability to sustain the change builds (CBT, mastery experiences, coaching).
Intervention strength I — motivational interviewing, reminders, social support; raises both the decisional balance (more perceived pros vs. cons) and the SE growth ceiling.
Relapse risk ρ — baseline chance of slipping from Action or Maintenance back to Contemplation; low self-efficacy amplifies it, matching the model's emphasis on relapse as a normal loop rather than a failure endpoint. A relapse always returns to Contemplation — the TTM's "spiral" rather than linear path — and agents never skip a stage forward.

This is the same five-stage model (Precontemplation → Contemplation → Preparation → Action → Maintenance) used in real smoking-cessation, exercise-adoption and medication-adherence interventions.

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