One-sigma statistical uncertainties due to small-number statistics in the fitted velocity dispersion as a function of the sample size N for single-epoch observations of a cluster with a velocity dispersion of 5 km   s^-1. The colors indicate the set of orbital parameter distributions used to generate the data and assumed for the fit: blue line for Sana et al. (2012); green line for Sana et al. (2013); red line for Kiminki & Kobulnicky (2012). The color-coding is the same as in Fig. 4. The statistical uncertainties are given relative to the input velocity dispersion of 5 km   s^-1. Every point in this graph represents the average statistical uncertainty (as measured by the MCMC) in 60 Monte Carlo simulations, except for sample sizes smaller than or equal to 30, where 200 Monte Carlo simulations were averaged.