Hi Harriet,
The 23 value came from the Leddy article (https://pmc.ncbi.nlm.nih.gov/articles/PMC3178037/) -(just above the discussion section. I find most articles don’t use the correct scoring guidelines for the Mini-BESTest and use a total score of 32 instead of 28. The Leddy team found that a score of 23 maximized sensitivity to minimize the likelihood of false negatives (mis-classifying someone as a non-faller when they are at risk of falling). There are a variety of numbers available in the literature (16, 19, 20, 21), so I think having a general feel for the Mini-BESTest and being able to eyeball if someone is in a falls risk range is sufficient for NCS purposes.
There is another article in community-dwelling elderly (not PD) that has cut-offs by decade: https://pubmed.ncbi.nlm.nih.gov/31162155/. Cut-off for 60-69 is 25, 70-79 is 23, 80-89 is 22, and 90+ is 17.
Chrissy