On parallel and serial (dis‐)aggregation in system dynamics models

Abstract

Compartment models are widely used in system dynamics to analyze complex systems. However, determining an appropriate level of aggregation remains a methodological challenge. This paper explores how parallel and serial (dis‐)aggregation affect a model's ability to reproduce dynamics of interest, using the beer distribution game (BDG) as a case study. We review existing aggregation guidelines that emphasize similarity of decision rules, flow purpose, and residence times, and assess their completeness through comparative simulations of (dis‐)aggregated BDG models. Our results suggest that while these guidelines are generally useful, they are incomplete: symmetry of flows in parallel structures emerges as an additional, previously neglected criterion, and including fast dynamics in models focused on long‐term behavior may add excessive detail without improving insight. These findings provide an initial step toward guiding modelers in balancing model simplicity and usefulness and motivate further research on whether, how, and why they extend beyond the BDG.