A proposed index system for reporting rabies rapid fluorescent focus inhibition test titres

In a trial to test the immunogenicity and the safety of a rabies human diploid vaccine it was found that the geometric mean titre (GMT) of individuals immunized with other rabies vaccines within two years of the trial was statistically significantly smaller than the GMT of individuals immunized with other rabies vaccines more than two years prior to the trial (Scheffé test, 5% level of probability). Since this result was unexpected, an unplanned analysis of the data was undertaken. Rapid fluorescent focus inhibition titres are expressed as international units per milliliter of serum (IU/ml). The IU/ml titres, based upon logarithmic calculations, are a coarse arithmetic measurement. A proposed index system for these titres smooths out this coarseness and permits meaningful statistical comparisons.