(14)The calculation of the default rate should meet certain requirements in order to ensure that it is comparable across ECAIs. For example, it should be measured over a 3-year time horizon in order to allow the observation of a significant number of defaults when risk is very low and it should account for withdrawals to avoid an underestimation of risk. In addition, it should include neither public sector ratings nor issue ratings, given the scarcity of defaults for the former type of ratings, and to avoid biasing the default rates towards issuers with higher number of issues by using the latter ratings.