The consequences of how subject matter expert estimates are interpreted and modelled, demonstrated by an emergency department des model comparing triangular and beta distributions

The aim of this paper is to demonstrate empirically the consequences of misinterpreting estimates from subject matter experts (SMEs), and to study the differences between modeling this with triangular and beta distributions. Three estimates which describe the duration of a process; minimum, maximum, and mode, is ideally sufficient as a proxy for the empirical distribution. However, these estimates might be biased when the SMEs confuse the difference between mean and mode. The analysis are performed in an ED model of a Norwegian hospital. When comparing the model output with data from the electronic patient record we see that a model with beta distributions based on the SME estimates outperforms a model with the more frequently used triangular distributions. A triangular distribution will overestimate the mean of the distribution compared to a beta distribution. We therefore encourage the use of beta distributions over triangular for activities with skewed distributions.