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How deep is knowledge tracing?

Paper · 2016 · Khajah

Summary

Khajah, Lindsey and Mozer investigate why deep knowledge tracing (DKT), an LSTM-based recurrent network for predicting whether a student will answer the next exercise correctly, was reported to beat Bayesian knowledge tracing (BKT), the field's standard hidden Markov model, by a wide margin. They did not dissect DKT. Instead, they proposed four kinds of structure in student data that classic BKT ignores: recency effects, the ordering of trials across skills, similarity between skills, and differences in individual ability. They then gave BKT extensions already described in the literature: forgetting, latent student abilities and automatic skill induction. They compared the extended BKT with DKT on four data sets: Assistments, Synthetic, Spanish and Statics. On average, the extended BKT matched DKT. Part of DKT's originally reported advantage appears to come from inconsistent evaluation. The authors conclude that DKT gains its edge from flexibility, not from discovering new representations. Interpretable, shallow models can therefore compete with deep ones in knowledge tracing.

Key points

  • Re-running BKT gave much higher AUCs than those reported in the original DKT paper (Piech et al.): 0.73 vs 0.67 on Assistments and 0.62 vs 0.54 on Synthetic. This points to an evaluation bias against BKT.
  • The models differ greatly in size. With 200 LSTM units and 50 skills, DKT has roughly 250,000 parameters, while BKT needs about 200.
  • On a scaled AUC measure, the enhanced BKT and DKT traded wins:
    • Enhanced BKT beat DKT by 20.0% on Synthetic and 3.0% on Spanish.
    • It trailed DKT by 8.3% on Assistments and 3.5% on Statics.
  • Each data set benefited most from a different extension:
    • Forgetting helped most on Assistments.
    • Skill discovery helped most on Synthetic.
    • Latent student ability helped most on Statics.
  • Forgetting and ability are cheap to add, whereas skill discovery requires costly MCMC inference. In exchange, the extended BKT keeps psychologically meaningful parameters and produces an explicit mapping of exercises to skills.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

 Fields, topics and concepts

Cite

Cite as Khajah. 2016. How deep is knowledge tracing?. arXiv (Cornell University).

The paper itself, not this page. BibTeX from the library's record of the work. arXiv 1604.02416

@misc{khajah2016how,
  title = {{How deep is knowledge tracing?}},
  author = {Khajah},
  year = {2016},
  eprint = {1604.02416},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/1604.02416}
}

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