95% Bayesian confidence intervals of substitution rate and root age using the coalescent prior and a strict molecular clock on 50 simulated data sets. Parameters are estimated using BEAST for 50 replicates under a strict molecular clock and a coalescent tree prior. Intervals that do not include the true value (blue line) are shown in red. Nucleotide substitution rate (a) and root age (b) inferred using a constant size tree prior. Nucleotide substitution rate (c) and root age (d) inferred using the Bayesian skyride method.