CFS Classification Tree

Scoring the Clinical Frailty Scale (CFS) requires clinical judgment. Increased uptake of the CFS internationally – bolstered by the recent COVID-19 pandemic – has led to the CFS being used by many health care professionals who do not have formal training in frailty care. While the CFS generally has very good inter-rater reliability, CFS scoring by inexperienced raters may not reflect expert judgment. For these novice raters, we developed a classification tree to simplify CFS assessment.

This classification tree is not intended to replace the CFS or clinical judgement. It may not be useful to experienced CFS raters, but it can aid in routine CFS scoring for inexperienced raters. Even so, raters using the classification tree should confirm whether their clinical judgement agrees with the CFS score derived by the classification tree. If the rater does not agree with the CFS level proposed for their patient by the classification tree, they should use clinical judgement to determine the appropriate CFS level. In a prospective study of 115 older adults assessed in an emergency department, the level of frailty derived using the classification tree matched the CFS score assigned by an experienced geriatrician in 63% of the cases; an additional 30% agreed within +/- one level (Theou et al., 2021).

The CFS classification tree can be navigated using routinely collected clinical data. If routine data are not available, raters can use a questionnaire we developed to collect the data needed to navigate the classification tree and arrive at a CFS score. The full questionnaire allows raters to record information about specific health conditions. There is also a short version of the questionnaire that captures information about health conditions in aggregate (e.g. the total number of health conditions). Both versions assess the same health domains.

In addition to the paper form, the questionnaire (in its full and short versions) can be accessed as an online tool with the classification tree algorithm embedded. Using the online tool, users are prompted to respond to questions until the algorithm collects enough information to propose a CFS score. The online tool does not save or store data.


Theou O, Pérez-Zepeda MU, van der Valk AM, Searle SD, Howlett SE, Rockwood K. A classification tree to assist with routine scoring of the Clinical Frailty Scale. Age Ageing. 2021;50:1406-1411.