(22)With regard to risk quantification, it is desirable that the PD estimates are relatively stable over time in order to avoid the excessive cyclicality of own funds requirements. Competent authorities should verify that the PD estimates are based on the long-run average of yearly default rates. In addition, as the own funds should help institutions survive in a time of stress, the risk estimates should take into account the possible deterioration in the economic conditions even in the times of prosperity. Finally, whenever there is an increased uncertainty that results from insufficient data, competent authorities should verify that an additional margin of conservatism has been adopted. If the length of available time series does not encompass the expected variability of default rates, appropriate methods should be adopted to account for the missing data.