Single Loss Expectancy (SLE) represents an organization's loss from a single threat. Which of the following formulas best describes the Single Loss Expectancy (SLE)?

Question

Options

• ASLE = Asset Value (AV) * Exposure Factor (EF)
• BSLE = Asset Value (AV) * Annualized Rate of Occurrence (ARO)
• CSLE = Annualized Loss Expectancy (ALE) * Annualized Rate of Occurrence (ARO)
• DSLE = Annualized Loss Expectancy (ALE) * Exposure Factor (EF)

• A
  90% (26)
• B
  7% (2)
• D
  3% (1)

Explanation

Option A is correct because SLE measures the monetary loss from a single occurrence of a threat, calculated by multiplying what an asset is worth (AV) by the percentage of that asset destroyed or compromised in the event (EF). For example, a $100,000 server with a 40% exposure factor yields an SLE of $40,000.

Why the distractors are wrong:

• B confuses SLE with ALE - multiplying AV by ARO gives you Annualized Loss Expectancy, not a single-event loss.
• C inverts the ALE formula; ALE = SLE × ARO, not the other way around, and mixing ALE with ARO produces a nonsensical circular calculation.
• D is also wrong because ALE already incorporates frequency (ARO); multiplying it again by EF double-counts factors and doesn't correspond to any standard risk formula.

Memory tip: Think of SLE as a snapshot - one event, one asset. The formula only needs two "one-time" values: what it's worth (AV) and how badly it's hit (EF). Once you multiply SLE by how often it happens (ARO), you get ALE - the annualized version.

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