Order Effects & Counterbalancing Lab (2D)

A within-subjects psychology experiment asks every participant to complete both a control and a treatment condition — which means the order they're tested in can leak into the results. This 2D simulator draws a virtual repeated-measures study as a live bar chart: each participant gets two bars, one per test position, colored by which condition landed there, with height driven by a transparent generative model (baseline ability + true treatment effect + order/practice effect + noise). A second chart plays the same underlying data forward participant-by-participant for both a fixed testing order and a counterbalanced design side by side, so you can watch the naive group-level estimate drift toward a biased asymptote in one case and converge on the true, ground-truth treatment effect in the other.