Exposure Rating

Reinsurance transfers part of an insurer's risk to another insurer, and pricing that transfer requires an estimate of the losses the reinsurer could pay under the treaty. Exposure rating approaches the problem through the portfolio's insured values, policy limits and other characteristics rather than relying only on its own past claims.

An insurer may have a new portfolio, a small number of large claims or insufficient years of reliable data, so its observed loss history may be a weak guide to the layer being priced, and an exposure-based method uses a broader view of comparable risks to estimate how losses could develop. The classic property approach expresses losses relative to insured values or policy amounts, because a loss of $100,000 means something different for a $120,000 building and a $10 million building.

Scaling losses to an exposure measure allows the model to connect severity patterns with the portfolio's distribution of values. An exposure curve describes how loss cost accumulates as the covered proportion of value increases; it is not simply the probability that a claim will occur, and the distinction between claim frequency and the share of total loss cost matters when allocating expected losses to insurance layers.

A reinsurance layer normally has an attachment point and a limit, and the reinsurer pays losses above the attachment up to that limit, subject to the treaty. Exposure rating estimates the share of losses expected to fall into that particular slice rather than treating every loss as fully reinsured.

Policy limits influence the estimate, because a large-loss layer receives little or no loss from policies whose limits cannot reach its attachment point, so a portfolio with more high-limit policies may have a different layer exposure even when its total premium matches another portfolio's premium. Selecting a curve requires judgment about the business being insured, since construction, occupancy, protection, location and coverage terms can change the loss pattern, and applying a curve from unrelated business can make an apparently precise calculation poorly matched to the real portfolio.

Exposure rating differs from experience rating, which begins with the portfolio's actual loss record and adjusts it for relevant changes. Exposure rating can estimate a layer with limited direct claims, but it still relies on empirical evidence or assumptions drawn from other risks.

Comparing the two approaches can reveal changing limits, weak data or an unsuitable model, so investigate a large disagreement rather than selecting whichever produces the preferred price. Expected loss is not the whole premium, because expenses, uncertainty, profit requirements and the cost of supporting the risk can affect pricing.

A reinsurer should not present a modelled loss estimate as if it were the final commercial price without those other considerations. For a non-finance manager, request the portfolio characteristics, chosen curve, attachment and limit, and the reason the model is considered suitable.

Ask how the estimate changes if insured values or severity assumptions are wrong. The model offers a structured estimate, not certainty about which claims will occur.