Certainty-Based Marking (CBM)

Confidence- or certainty-based assessment in various guises has a long history, and is surprisingly under-used. When properly set up, it motivates students to think carefully about whether they can see reasons for either sound justification or uncertainty about the answers they give in tests. It is particularly helpful as a study aid in self-tests, providing a stimulus and challenge, and a warning signal when misconceptions have arisen. But it has also been clearly shown to improve the statistical reliability and validity of assessment data.

CBM marks I implemented CBM at UCL in 1994 for my own teaching in physiology, medicine and maths. The principles and outcomes are set out in my teaching publications. UCL currently promotes Moodle (where I have also incorporated CBM), but for self-tests I much prefer the more versatile software ( LAPT ) that I initially developed for UCL and that is now sited here. It continues to host around 60,000 sessions per year, mostly for students of UCL and Imperial College London.


CBM Self-Tests
The CBM Self-Tests site hosts new software updated and improved from the LAPT system at UCL, which has served millions of questions per year to students at London universities and elsewhere. It is designed to run efficiently offline on computers or tablets, enabling students to engage in private study with the option to upload and view data, enter comments and discussion in context, download additional exercises, etc. from their institution's server. For self-test purposes it offers better facilities and feedback than Moodle. Staff can view the data that students upload (either anonymously or under their own userid) and can deal with comments raised; but it is important for self-tests that students appreciate that this is a learning experience not an assessment, that they learn through mistakes, and that whether self-test mistakes are visible or in private they will never be used as evidence against them.


Using CBM in Moodle
CBM has been implemented in core Moodle code since version 2.6 (2013), see Using certainty-based marking in Moodle. For staff reports, it is essential to install the appropriate CBM Grades PLUGIN. In addition, there are downloadable code modifications available here that substantially enhance CBM performance and feedback to students compared with core code up to the present. These code mods are also available to fully implement CBM as far back as v 1.9 (2007). Each download contains a few files to replace core Moodle files in an appropriate version. No adverse events have been reported from installing any of these downloads, and the changes can be easily reversed by overwriting altered files with the supplied original versions.

Links (opening in a separate window or tab) Any comments, suggestions or questions: please don't hesitate to email.

Prof. Tony Gardner-Medwin
Emeritus Prof. of Physiology, UCL Div. of Bioscience ucgbarg@ucl.ac.uk
June 2016