A dollar range in which an insured or, in the case of an insurer's book of
business, a group of insureds is expected to experience a fairly high level of
loss frequency. This is the layer typically subject to deductibles,
self-insured retentions (SIRs), retrospective rating plans, and similar
programs. Sufficient loss frequency in the working layer allows many
organizations to provide some degree of statistical credibility to actuarial
forecasts of the total expected losses during a specific period of time—for
example, 1 year.