A product-liability underwriter can charge per unit sold, per $1,000 of sales, or per employee. All three are measurable, but only one tracks how risk actually grows. Choosing among candidates, and defending the pick, is the skill this lesson drills.
An exposure base is the unit premium is charged per. Choosing one means comparing candidates against three tests. A common study heuristic weighs them unequally, though the source itself ranks none of the three.
KEY: Proportional to expected loss, practical, and consistent with precedent. As a study heuristic you can treat practicality as a pass/fail gate and proportionality as the tie-breaker among survivors, but the source does not rank the criteria. Precedent can by itself block an otherwise better base.
Proportional to expected loss. As the base doubles, expected loss should roughly double. Payroll works for workers comp because more payroll means more worker-hours and more injury exposure. This is the criterion candidates most often split on, so it usually decides the winner.
Common mistakes
- Ignoring practicality when a base is loss-proportional. A perfectly loss-proportional base that the insured can understate is still disqualified. As a study heuristic, run practicality as a gate before you rank on proportionality.
- Defending a base by praising it in isolation. A defense must beat each rival on a named criterion, not just list virtues of the winner.
- Picking headcount for workers comp. Two firms with equal headcount but different payrolls carry different risk; headcount fails proportionality.
Bottom line
- A good exposure base clears three tests: proportional to expected loss, practical (objective, cheap, verifiable, hard to manipulate), and consistent with historical precedent.
- As a study heuristic you can treat practicality as the gate and proportionality as the tie-breaker, but the source ranks none of the three, and precedent alone can block an otherwise better base.
- A base change carries three transition costs: large premium swings for individual insureds, rating algorithm and systems rework, and significant data adjustments for future analyses.
- Auto uses car-years, workers comp uses $100 of payroll, homeowners uses house-years, general liability and products use sales or receipts, physicians use per-doctor counts.
Exam shortcut
When a scenario lists candidate bases, run practicality first as a pass/fail filter, then rank the survivors by proportionality to loss. Treat this ordering as a study heuristic, and remember precedent alone can block an otherwise better base. To reject a candidate in one sentence, name the criterion it violates and the two risks it misprices ("equal headcount, unequal payroll"). Graders reward the specific mispriced pair, not vague criticism.
The full lesson (about 2,222 words, 15 min read) adds 2 worked examples, all 6 common mistakes, a self-check, free in the app.
Learning objectives
- A2
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