Left panel: marginal likelihood estimated by the Perrakis method vs. sample size for three models: a single Keplerian plus white noise (k1; blue), a quadratic drift plus white noise (k0d2; green), and pure white noise (k0; orange). The one-Keplerian model is clearly favoured by the data. The error bars correspond to the 95% confidence interval. Right panel: histogram of 1000 Monte Carlo realisations of the Bayes factor between model k1 and k0 (orange) and k0d2 (green); the solid curves are normal distributions with the mean and variance equal to those of the Monte Carlo sample.