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Using a return-tail sign in a loss quantile

A lower return tail becomes an upper loss tail under the negative linear loss transformation.

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Read the original conversion

For fixed starting value 1,000,000, a normal return with mean 1% and dispersion 2% produces mean loss −10,000 and dispersion 20,000. Using −z95 directly in the upper loss formula would select the opposite side of the loss law.

Use the stated loss-side confidence

The 95% loss quantile is −10,000+20,000×z95≈22,897.072539. Equivalently, the lower 5% return quantile is 0.01−0.02×z95; applying −V to that return yields the same loss amount.

Retain the direction record

Tail-direction check
Modeled quantityAdverse tail
Positive returnLower return tail
Positive lossUpper loss tail
Transformation L=−VrReverses order for V>0

Do not fix a sign by taking an absolute value

An absolute-value repair can hide a mistaken tail direction or remove a legitimate negative loss summary. Establish the sign convention and the linear transformation before interpreting the number.

Further references