Characterizing Distributions by Moment Existence and Tail Behavior

Free SOA Exam FAM (Fundamentals of Actuarial Mathematics) lesson in Severity, Frequency, and Aggregate Models. 9 min read, ~1,406 words.

Pareto: iff. Alpha is a ceiling on moment order. Heavy-tailed: MGF does not exist for any. Pareto, lognormal, Weibull( ). Light-tailed: MGF exists for some. Exponential, gamma, Weibull( ). Lognormal is the key edge case: all moments finite, but still heavy-tailed (no MGF). Hazard rate: DHR = heavy tail, IHR...

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