Posted on November 28, 2016 in
Proposals to add more terms to the modified Arrhenius fitting (with an exponential dependence on reciprocal temperature and water activity) used with ASAPprime® run the risk of over-fitting limited data sets. Over-fitting of accelerated data is particularly dangerous compared to common DOE optimizations since the optimized parameters are used in extrapolated fitting, where small errors can exaggerate behavior. The scientific basis for the moisture-modified Arrhenius equation is reviewed. Any added fitting term also has the disadvantage of reducing the fitting degrees of freedom. Reasons why an apparent cross-term between temperature and RH is observed include carrying out stability studies in packaging rather than open and not following an isoconversion process. The current ASAPprime® method has been shown to be accurate in virtually all systems examined to date (where no phase boundary was crossed).