THE FORMALIN TEST - A VALIDATION OF THE WEIGHTED-SCORES METHOD OF BEHAVIORAL PAIN RATING

The formalin test was developed using an ordinal scale of weighted sco res to rate the intensity of pain-related behaviours in animals. Howev er, no studies have been carried out to establish the ordinal relation ship of the behavioural categories used to generate the weighted pain intensity scores. The purpose of the present study was to evaluate the validity of the weighted-scores technique by assessing the ordinality of the behavioural categories associated with the specific category w eights. The amount of time spent in each of 4 behavioural categories w as measured as a function of the concentration of the formalin solutio n injected into the hindpaw of rats, and as a function of the dose of systemic morphine given to rats injected with a concentrated (5.0%) so lution of formalin. The ordinal nature of the category weights was sup ported when the data were subjected to a polychotomous logistic regres sion for fitting an ordinal model.