Date of Original Version
Abstract or Description
Modeling students’ knowledge is a fundamental part of intelligent tutoring systems. One of the most popular methods for estimating students’ knowledge is Corbett and Anderson’s  Bayesian Knowledge Tracing model. The model uses four parameters per skill, fit using student performance data, to relate performance to learning. Beck  showed that existing methods for determining these parameters are prone to the Identifiability Problem: the same performance data can be fit equally well by different parameters, with different implications on system behavior. Beck offered a solution based on Dirichlet Priors , but, we show this solution is vulnerable to a different problem, Model Degeneracy, where parameter values violate the model’s conceptual meaning (such as a student being more likely to get a correct answer if he/she does not know a skill than if he/she does). We offer a new method for instantiating Bayesian Knowledge Tracing, using machine learning to make contextual estimations of the probability that a student has guessed or slipped. This method is no more prone to problems with Identifiability than Beck’s solution, has less Model Degeneracy than competing approaches, and fits student performance data better than prior methods. Thus, it allows for more accurate and reliable student modeling in ITSs that use knowledge tracing.