The operating level is the dollar range in which an insurer, or in the case of an insurer’s business book, a group of insurers, is expected to experience a fairly high level of loss frequency. This is the level to which deductibles, self-insured retentions (SIRs), retrospective rating plans, and similar programs typically qualify. Sufficient loss frequency in the working layer allows many entities to provide some degree of statistical confidence in actuarial projections of total expected losses over a specified time period, such as 1 year.