Top: posterior probability ﹩P\left({I}_{b}| {n}_{b},{N}_{p},{\rm{\Delta }}t\right)﹩ after observing two outbursts in 319 protostars over a 6.5 yr window as a function of outburst interval. The probability peaks at about 1040 yr (red dotted–dashed line). Dotted lines illustrate the 90% confidence interval, which is from 690 to 40,300 yr. Bottom: the cumulative probability distribution, which further illustrates the confidence interval.