Abbott's formula

Definition

A statistical correction used to adjust observed mortality in treated experimental groups by subtracting background mortality occurring in untreated control groups, typically expressed as: corrected mortality (%) = [(mortality in treated - mortality in control) / (100 - mortality in control)] × 100. The formula assumes control mortality is independent of treatment effects and does not exceed 20 percent.

Etymology

Named for entomologist W. S. Abbott, who published the method in 1925 for analyzing insecticide trial data.

Example

In a mosquito larvicide bioassay, if the untreated control vial shows 15% pupal mortality due to handling stress while the treated vial shows 65% mortality, Abbott's formula yields corrected mortality of [(65 - 15) / (100 - 15)] × 100 = 58.8%, isolating the true insecticidal effect from background losses.

Synonyms

• Abbott's correction
• Abbott correction

Related Terms

• corrected mortality
• probit analysis
• LC50
• Bioassay
• control mortality
• dose-response

Usage Notes

Apply only when control mortality is greater than zero but less than 20%; above this threshold, the independence assumption fails and experimental repetition is advised. The formula is specific to percentage data and should not be used with raw counts without conversion. Results may be labeled 'percent control' or 'efficacy' in agricultural entomology literature, though these terms sometimes omit explicit mention of Abbott correction.