Optimal scoring strategies and weights for the formalin test in rats

The formalin test is a well-established model for assessing inflammatory nociceptive processes and analgesic drug effects. Previous research established the validity of an ordinal relationship among three well-defined pain behavior categories used to compute a composite pain score (CPS). However, optimal weights had not been validated. The present research used data from Coderre et al. (1993) and from Sufka and Roach (1996) to determine and validate optimal pain behavior category weights. Based on multiple regression analyses and Pearson correlations, optimal weights of 1 and 2 are proposed for behavior categories 2 and 3, respectively; behavior category 1 is not scored. These results are consistent with the work of Abbott et al. (1995) and Coderre et al. (1993) in that the ordinal relationship among category weights is preserved, and extend previous work by establishing optimal category weights.