standard method to pool such varying descriptive statistics of the distribution of a variable (age at onset of mental disorders) when the variable of interest follows a non-normal distribution and/or is heterogeneously censored. Therefore, we have developed an ad-hoc method to meta-analyse these estimates. To assess these co-primary outcomes, we first estimated the histogram of the age at disorder onset that minimised the sum of squared errors (SSE) of the study-reported data. From this histogram, we then derived peak age at onset, as well as the proportion of individuals showing an onset before 14, 18 and 25 years of age, and the 25%, 50% and 75% percentiles of the age at disorder onset. Thereafter, we used an empirical bootstrap approach [34] to estimate the 95% confidence intervals of age at onset.
