How rapidly do people forget practical knowledge?

This is an intentionally quite vague question.

In Quantum Country: QCVC questions are initially forgotten at very different rates

A more conservative figure in medicine:

Medical students forget roughly {25–35} percent of basic science knowledge after {one year}, more than {50} percent by {the next year} (Custers, 2010), and {80–85} percent after {25 years} (Custers & ten Cate, 2011).

(via Mozer, M. C., & Lindsey, R. V. (2016). Predicting and Improving Memory Retention: Psychological Theory Matters in the Big Data Era. In M. N. Jones (Ed.), Big data in cognitive science (pp. 34–64).)

Reading natural text in a contrived experimental setting, Amlund et al (1986) find <50% free recall minutes later, even when readers knew it was a test.


Amlund, J. T., Kardash, C. A. M., & Kulhavy, R. W. (1986). Repetitive Reading and Recall of Expository Text. Reading Research Quarterly, 21(1), 49.

Custers, E. J. F. M. (2010). Long-term retention of basic science knowledge: A review study. Advances in Health Sciences Education, 15(1), 109–128.